Tafsir of Al-Anbiya' 21:94

"So whoever does [some] of the righteous deeds..."

His saying, "So whoever does [some] of the righteous deeds," is an elaboration of the recompense; that is, whoever performs righteous deeds, or a portion of righteous deeds, "while he is a believer" in that which it is obligatory to believe in, "then there is no denial of his effort." That is, there is no deprivation of the reward for that deed. It is expressed as kufran (denial), which is the concealing and rejection of a favor, to manifest the perfection of His, the Exalted’s, transcendence above it, by depicting it in the form of what is impossible to proceed from Him, the Glorified, regarding vile acts, and by presenting the act of rewarding as if it were a matter incumbent upon Him, the Exalted. The negation of the genus, which signifies generality, is used for the sake of hyperbole in demonstrating His transcendence. It is apparent that the structure is after the fashion of, "There is no preventer for what You have given," and the discussion regarding this is well-known among the scholars of the Arabic language. He expressed the deed as "effort" (sa'y) to show that it is held in high regard. In the reading of 'Abdullah, it is "then there is no kufr," and the meaning is the same. "And indeed We are, for him," that is, for his effort—though it is said the pronoun refers to the one [doing the deed], but that is of no consequence—"recorders."

That is, We are recording it in the register of his deeds so that it is not lost in any way. The verse is used as evidence that the acceptance of a righteous deed in an absolute sense is conditional upon faith, and this is the opinion of some. Others have said: Faith is a condition for the acceptance of those deeds that require an intention. The verification of this is in its proper place.