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man jāʾa bi-l-ḥasanati fa-lahū ʿashru ʾamthālihā wa-man jāʾa bi-s-sayyiʾati fa-lā yujzā ʾillā mithlahā wa-hum lā yuẓlamūna
Whoever brings virtue shall receive [a reward] ten times its like; but whoever brings vice shall not be requited except with its like, and they will not be wronged.
— Ali Quli Qarai
Surah Al-‘An’am, Verse 160
160. "Whoever brings a good (deed), he shall have ten times its like, and whoever brings vice, he shall not be recompensed but with its like, and they shall not be dealt with unjustly."
In this holy verse the multifold reward given for good deeds is referred to. Through previous verse, the wrong doers were threatened and reprimanded upon their evil deeds, while here, in this verse, the Qur'an clearly says:
But as for those who commit a sin, Allah will punish them equally as much as their sin. As a result of the greatness of His grace and generosity, Allah bestows the reward of a good action more than it's due, and forgives the faults of the sinners. And, if he punishes one, He punishes as much as the one deserves, not more than that. The verse continues saying:
Some of the commentators believe that the purpose of the Qur'anic word /hasanah/ (a good deed) is 'Unity', and the purpose of the word /sayyi'ah/ (a vice) is 'infidelity'. According to this meaning, the essence of good deeds is Unity and the essence of vices is infidelity.
There win not be done any unjust against anybody, because none will be punished more than what one deserves. Therefore, Allah treats with His grace when He gives reward, but He treats with His justice when He punishes. The tenfold rewards that He gives for a good action, only one part is the wage of it and the rest nine parts are 'Allah’s grace'. Surah An-Nisa. No.4. Verse 173 says:
It is worthy to note that the tenfold reward is for all believers in general, but some deeds which are done in some circumstances by some qualified persons will be bestowed up to seven hundred times rewards, and even without measure rewards either.