The Reckoner, The Sufficient, The one who Suffices.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Haseeb (in Arabic: ٱلْحَسِيبُ). He is The One who takes account of all actions and reckons them on the day of judgment. There is nothing that goes unnoticed, however small. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the one who will take account of everything and will hold each person accountable. He will give whatever is sufficient and necessary in every situation.
From the root ha-sin-ba (ح س ب), which has the following classical Arabic connotations: To reckon, number, count, calculate, compute, think. To give without sparing or scanting, to give without the receiver’s expectation. To suffice, to be sufficient, or without measure.
Al-Muqeet and Al-Haseeb:
The previous name we discussed is Al-Muqeet which is closely related to Al-Haseeb. Al-Muqit is The Nourisher. He provides for our sustenance in a variety of ways - both material and spiritual. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ has given each one of us a varying degree of intellectual ability as well as a certain amount of wealth and time to spend however we wish.
Now, Hasib comes from hasaba, which means to count (past tense), calculate, or account. He is the one who measures and reckons. So, in a way, Al-Muqeet is the one who fills us with life, knowledge, and wealth, and Al-Haseeb is the one who is constantly measuring. He is checking to see whether these gifts are squandered or utilized. So, in the perpetual form, Al-Hasib is "The Accountant," who watches every action and deed and will settle all accounts.
Allazeena yuballighoona Risaalaatil laahi wa yakhshaw nahoo wa laa yakkhshawna ahadan illal laah; wa kafaa billaahi Haseebaa
"[Allah praises] those who convey the messages of Allah and fear Him and do not fear anyone but Allah. And sufficient is Allah as Accountant." — (Qur'an 33:39)
Al-Haseeb is also understood to be a name of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ that demonstrates the attribute of His knowledge. He knows the result of every creation. Nothing surprises Him. On the day of reckoning, they will stand before Him bringing their accounts of whatever good they've accumulated. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ does not need to perform any calculations. He knows the result. There is no inaccuracy or impreciseness in His judgment. He takes everything into account and does not miss any detail.
Another meaning of Al-Hasib is sufficiency. He is sufficient, not needing anyone or anything. Nothing is truly self-sufficient besides Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. If something were self-sustaining, it would not need anything for its existence. There is nothing but Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ that posseses this quality. But yet, a common desire is to be self-reliant, but this term is often misused and misunderstood. What we really mean is we need Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ to take care of us and help us in our affairs. We are not to be beholden to anyone or anything but Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. In Surah Talaq verse 3, "And will provide for him from where he does not expect. And whoever relies upon Allah – then He is [hasbuh] sufficient for him."
Du'a of Prophet Muhammad ﷺ:
The best example of this is when the Prophet ﷺ faced a loss in battle Uhud against Abu Sufyan. The army gathered and confronted the Prophet (may peace be upon him), and in an attempt to break their morale, "Men said to them: 'A great army is gathering against you' And frightened them: But it (only) increased their Faith: They said: Hasbunallah wa ni’mal-Wakil "For us Allah sufficeth, and He is the best disposer of affairs." (Qur'an 3:173)
Wa nada’ul mawaazeenal qista li Yawmil Qiyaamati falaa tuzlamu nafsun shai’aa; wa in kaana misqaala habbatim min khardalin atainaa bihaa; wa kafaa binaa haasibeen
"And We place the scales of justice for the Day of Resurrection, so no soul will be treated unjustly at all. And if there is [even] the weight of a mustard seed, We will bring it forth. And sufficient are We as accountant." — (Qur'an 21:47)
From this attribute of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ we can learn not to undermine any act of good. There is no deed too small. Any chance to do good should be taken with utmost urgency because, on the day of reckoning, we would wish to have a chance to replay those moments and do things differently. So this name reminds us not to waste a moment to do good and go the extra mile because most people won't. Be an extraordinary individual, always looking and observing to find a way to help people. Don't squander your time on earth as 'The Accountant' is watching how you spend the greatest capital of all, which is your time.
Be courteous, and don't be afraid to be different. Run to the kitchen the next time someone says they are thirsty and see how weirdly they'll look at you. Another example the Qur'an teaches us is to greet the person who says salam with one that's better than it (i.e., Assalamualaikum being the base, Assalamualaikum Warahmatullah being one greater, and Assalamualaikum Warahmatullahi Wabarakatuh being the greatest of them all). Imagine the strange looks if, in the English language, we did the same. Your friend says, "Hey," and you respond, "Hi, hope you're doing better than good and better than most, May Allah shower His peace and blessings upon you!"
Now, in every interaction, you're given a chance to have that same effect, not just with being over the top with your words but with your presence, alertness, attention, and overall care for the other person. When someone really cares, we can feel it. It's an intuitive feeling and hard to fake. But it can be worked on and improved. What if this was your last conversation with that person? How would that change the dynamics of the way you approach the interaction?
Mai yashfa shafaa'atan hasanatay yakul lahoo naseebum minhaa wa mai yashfa shafaa'atan saiyi'atany-yakul lahoo kiflum minhaa; wa kaanal laahu alaa kulli shai’im Muqeetaa Wa izaa huyyeetum bitahaiyyatin fahaiyoo bi ahsana minhaaa aw ruddoohaa; innal laaha kaana alaa kulli shai'in Haseeba
"Whoever intercedes for a good cause will have a reward therefrom; and whoever intercedes for an evil cause will have a burden therefrom. And ever is Allah, over all things, a Keeper. And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]. Indeed, Allah is ever, over all things, an Accountant." — (Qur'an 4:85-86)
Ibn Mas'ud narrated that the Messenger of Allah SAW said: "The feet of the son of Adam shall not move from before his Lord on the Day of Judgment, until he is asked about five things: About his life and what he did with it, about his youth and what he wore it out in, about his wealth and how he earned it, and spent it upon, and what he did with what he knew." 
 Classified as hasan by al-Albaani: Jami at-Tirmidhi 2416