990 - Ishaq ibn Ibrahim narrated to us, he said: Safwan ibn 'Isa narrated to us, he said: Ibn 'Ajlan narrated to us, from Zayd ibn Aslam, from 'Ata' ibn Yasar, from Abu Sa'id al-Khudri, from the Prophet (peace be upon him) who said: "If one of you is in doubt during his prayer and does not know whether he prayed three or four, let him cast away the doubt and proceed upon certainty. If it was a fifth (rak'ah), the two prostrations will make it even (shafa'at-ha); and if it was a fourth, the two prostrations are a humiliation (targhim) for the Satan."

991 - 'Isa ibn Sulayman narrated to us, he said: 'Abd Allah ibn Ja'far narrated to us, he said: Zayd ibn Aslam informed me, from 'Ata' ibn Yasar, from 'Abd Allah ibn 'Abbas, who said: The Messenger of Allah (peace be upon him) said: "If one of you is in doubt during his prayer and attains certainty that he has prayed three, let him pray one (rak'ah) with its bowing and prostrations, then let him recite the tashahhud. When he finishes and there is nothing left but to perform the taslim, let him perform two prostrations while sitting, then let him perform the taslim. If he had prayed three and the rak'ah he prayed was the fourth, the two prostrations are a humiliation for the Satan. And if he had (already) prayed four, the rak'ah he prayed was a fifth which the two prostrations have made even."