(The Total Provider)
The Provider, The Sustainer. The one who creates sustenance for all His creations.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Ar-Razzaq (in Arabic: ٱلْرَّزَّاقُ) The Provider, The Sustainer for all His creatures. He is The One who creates all means of nourishment and gives them their livelihood. He is the provider of growth for all things good for the body, the soul, and the mind.
From the root ra-zay-qaf (ر ز ق), which has the following classical Arabic connotations: to receive something beneficial, especially as a gift to be provided with the necessities of life, to receive a portion, share or lot, to be supplied with a means of subsistence.
The difference between Ar-Razzaq and Al-Wahhab:
There is often confusion between the names Al-Wahhab (The Bestower) and Ar-Razzaq (The Provider). Al-Wahhab contains the same root as the name Hiba, which means a gift. So, Al-Wahhab refers to Allah's attribute of being the perpetual giver of gifts. It knows no bounds and requires no action from the receiver. Now, rizq has multiple meanings; the first is of general sustenance. This refers to any physical or material wealth. It's what has been allocated by the creator for you. However, unlike a gift, effort must be applied to receive it. This encompasses the outward definition of rizq.
Rizq can also apply to inward sustenance - one that benefits your soul, your heart (emotional sustenance), your faith, and your health. When you count on Allah's سُبْحَٰنَهُۥ وَتَعَٰلَىٰ blessings, seek the rizq that will purify your soul, guide you, and increase your imaan for it is nobler. The inward sustenance is ever-lasting, whereas material provision, although necessary, is only temporary.
A lesson from Prophet Ibrahim (as):
In the Qur'an, Surah Ash-Shu'ara, Prophet Ibrahim (as) addresses Polytheists giving reasons why Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ should be the only one worthy of worship. He argues how it is Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, "Who created me and Who guides me; Who gives me food and drink, and Who, when I am ill, heals me; Who will cause me to die and then will again restore me to life." (Qur'an 26:78-81) What's interesting to note here is the order of things mentioned. Prophet Ibrahim (as) first shows appreciation for his existence and to be among those Allah guided. He only then shifts to the outward rizq of worldly provisions such as food, drink, and health.
The name mentioned in the Qur'an:
There are countless ayat which discuss Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ as being The Provider. For example, "Allah is the one who created you, then provided for you, then will cause you to die, and then will give you life. Are there any of your 'partners' who does anything of that? Exalted is He and high above what they associate with Him" (Qur'an 30:40) and also, "O mankind, remember the favor of Allah upon you. Is there any creator other than Allah who provides for you from the heaven and earth? There is no deity except Him, so how are you deluded?" (Qur'an 35:3) But as a reference to the name Ar-Razzaq there is only one instance:
Wa maa khalaqtul jinna wal insa illaa liya'budoon Maaa ureedu minhum mir rizqinw wa maaa ureedu anyyut'imoon Innal laaha Huwar Razzaaqu Zul Quwwatil Mateen
"And I did not create the jinn and mankind except to worship Me. I do not want from them any provision, nor do I want them to feed Me. Indeed, it is Allah who is the [continual] Provider, the firm possessor of strength." — (Qur'an 51:56-58)
The pairing of Ar-Razzaq and Al-Mateen:
The pairing here is with the two names Ar-Razzaq and Al-Mateen, the perpetual provider and the firm possessor of strength. We can always depend on Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ for provision because He is the firm one. What does it mean to be firm? It means being solid, unwavering, or unbreakable. You can forever rely on Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ because of His strength. All other sources that claim to be strong providers really are not. The greatest countries or empires all rise and fall, and the biggest companies of the past are now bankrupt. Nothing is ever-lasting except Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. He is unshakable.
Qul mai yarzuqukum minas samaawaati wal ardi qulil laahu wa innaaa aw iyyaakum la’alaa hudan aw fee dalaalim mubeen
"Say, 'Who provides for you from the heavens and the earth?' Say, 'Allah. And indeed, we or you are either upon guidance or in clear error.'" — (Qur'an 34:24)
Is your Rizq decreed?
It was Narrated Abdullah who recorded Allah's Messenger ﷺ as saying, "...then Allah sends an angel and orders him to write four things, i.e., his provision, his age, and whether he will be of the wretched or the blessed (in the Hereafter). Then the soul is breathed into him." 
If your rizq is decreed, why make du'a? This question is often asked, and it's rather a moot point. Allah's qadr (divine decree) is known only by Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. We don't know what was written, and as mentioned previously, to receive worldly rizq still requires genuine effort. We simply don't know; it could be after reading this, you make du'a asking from Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, and He increases what has been portioned for you. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ had already known this as it was in your qadr. It was written, but you did not know. So we proceed just as we would before, doing good deeds, making du'a, and putting our best foot forward. The rest is with Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ.
Amman haazal lazee yarzuqukum in amsaka rizqah; bal lajjoo fee utuwwinw wa nufoor
"Or who is it that could provide for you if He withheld His provision? But they have persisted in insolence and aversion." — (Qur'an 67:21)
At some biological level, we have this looming anxiety of not having enough. We're afraid of losing our job, being unable to pay our bills, or not having enough to eat. We live with this constant angst and worry.
The release can come from knowing Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Ar-Razzaq. He is the best provider for all; there is not a single creature that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ does not provide for. Since He is the only one who can give sustenance, we should seek it from Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. Understanding this frees a person from the shackles of the influence of an unjust employer, dictator, or any kind of authority. People may be coerced to compromise their morals and resort to cheating and stealing to secure sustenance. But the one who knows Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ as Ar-Razzaq will avoid acting in this way as he knows the absolute authority is with Allah, The Almighty.
Narrated Warrad: (the clerk of Al-Mughira bin Shu`ba) Once Al-Mughira dictated to me in a letter addressed to Muawiya that the Prophet ﷺ used to say after every compulsory prayer, "La ilaha illa l-lahu wahdahu la sharika lahu, lahu l-mulku wa lahu l-hamdu, wa huwa `ala kulli shay'in qadir. Allahumma la mani`a lima a`taita, wa la mu`tiya lima mana`ta, wa la yanfa`u dhal-jaddi minka l-jadd. [There is no Deity but Allah, Alone, no Partner to Him. His is the Kingdom and all praise, and Omnipotent is he. O Allah! Nobody can hold back what you gave, nobody can give what You held back, and no struggler's effort can benefit against You]." And Al-Hasan said, "Al-jadd' means prosperity [??]." 
The attitude which is best for a believer to adopt was mentioned in the hadith of Sahih Muslim. Abu Hurairah narrated that the Messenger of Allah ﷺ said: "Look at those who are beneath you and do not look at those who are above you, for it is more suitable that you should not consider as less the blessing of Allah."  This problem has multiplied a thousandfold in the age of social media. We see the highlight reel of everyone's best life. It then leads to shaitan planting his seeds of doubt in the garden of your mind. These weeds - if not dealt with immediately - take form and spread, soon overtaking the entire garden. This manifests in a variety of ways into doubt, resentment, or belittling the favors which Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ has given us (nauzubillah).
For those seeking tranquility, it is better to find contentment with that which Allah has already provided you. This sentiment is perfectly captured in Surah Ta-ha verse 131, "And do not extend your eyes toward that by which We have given enjoyment to [some] categories of them, [its being but] the splendor of worldly life by which We test them. And the provision of your Lord is better and more enduring."
It was narrated from Salamah bin ‘Ubaidullah bin Mihsan Al-Ansari that his father said: "The Messenger of Allah (ﷺ) said: 'Whoever among you wakes up physically healthy, feeling safe and secure within himself, with food for the day, it is as if he acquired the whole world.'" 
 Sahih al-Bukhari 6594
 Sahih al-Bukhari 844
 Sahih (Darussalam) Sunan Ibn Majah 4142
 Hasan (Darussalam) Sunan Ibn Majah 4141