[Ruling on one who prays and then finds at the end of the prayer that water has not reached a spot on his forearm]

Answer (and Allah is the One who grants success): If a Muslim performed wuḍūʾ as Allah, Exalted is He, commanded, then prayed and—at the end of the time—saw something like a small spot of dough or the like on his forearm under which water had not reached, what appears to me is that he is not required to wash that and repeat the prayer. That is because:
1. The scholars of the madhhab and others did not require a woman to remove what she places on her face for beautification, even though it prevents water from reaching what is beneath it; rather, they validated her prayer, adducing as evidence the customary practice of the Muslims.
2. It is not within human capacity to be completely free of error and forgetfulness. Hence Allah, Exalted is He, said: “And there is no blame upon you for that in which you erred, but [only for] what your hearts intended.” [al-Aḥzāb: 5].
If it is said: The legally responsible person does not exit the obligation due to forgetfulness; rather, he must perform the act in order to be discharged of the obligation.
We say: In the case before us, the legally responsible person did what he was commanded to do; he traced the effects of dough and the like on his limbs and removed them, and a speck eluded him such that he did not discover it until the end of the time—so his ruling is not that of one who forgot to do what he was commanded altogether. He has, in fact, complied with the command, taken care, and been thorough, and thus he has been discharged of the obligation; there is no blame upon him beyond his capacity.
3. It is said of one who acted thus that he “washed his hands up to the elbows” in both language and custom; hence we say that such wuḍūʾ is valid.
4. It is narrated from some scholars that washing most of the limb suffices—on the basis that, in the usage of the linguists, the majority of a thing is treated as the whole of it. If it is said: It is narrated that when the Prophet (may Allah bless him and his family and grant them peace) saw a man praying in the mosque, the Prophet said to him: “O man, I see the back of your heel dry; if you have touched it with water, then complete [your ablution],” so ʿAlī (peace be upon him) said to the Prophet (may Allah bless him and his family and grant them peace) —whose meaning is: “If this man prayed like this, would his prayer be valid?” He said: “No.” We say: The one who leaves the back of his heel dry is negligent in purification—careless and remiss; unlike the case before us, in which none of that occurred.