"If any of you becomes forgetful in his prayer and does not know whether he has prayed one or two [units], he should base it on one. If he does not know whether he has prayed two or three, he should base it on two. If he does not know whether he has prayed three or four, he should base it on three, and he should perform two prostrations before he concludes [the prayer]." It was recorded by al-Tirmidhī (1/80-81), Ibn Mājah (1209), al-Ṭaḥāwī (1/251), al-Ḥākim (1/324-325), and al-Bayhaqī (2/332), and Aḥmad (1/190) through the route of Muḥammad ibn Isḥāq from Makhūl from Kurayb from Ibn ʿAbbās from ʿAbd al-Raḥmān ibn ʿAwf who said: I heard the Prophet (ṣallá Allāhu ʿalayhi wa-sallam) say it, and he mentioned it. The wording is from al-Tirmidhī, who said: "A good, rare, authentic ḥadīth." So he said, but Makhūl and Ibn Isḥāq are known to obscure their sources, so how can it be good, let alone authentic?! Yes, Ibn Isḥāq did explicitly state the transmission in a narration for Aḥmad (1/193), but he sent it from Makhūl and connected it through another route. Aḥmad said: Ismāʿīl narrated to us, Muḥammad ibn Isḥāq narrated to us, Makhūl told me that the Messenger of Allāh (ṣallá Allāhu ʿalayhi wa-sallam) said: If any of you prays and doubts in his prayer... Ibn Isḥāq said: Ḥusayn ibn ʿAbd Allāh said to me: Did he narrate it to you with a chain? I said: No, he said: But he told me that Kurayb, the client of Ibn ʿAbbās, narrated it to him from Ibn ʿAbbās. Al-Bayhaqī also recorded it and said afterward: "The connection of the ḥadīth became attributed to Ḥusayn ibn ʿAbd Allāh, who is weak, but it has a supporting narration from Makhūl." Meaning from Kurayb with it. Then he and al-Ḥākim (1/324) recorded it through two routes from ʿAbd al-Raḥmān ibn Thābit from his father from Makhūl with it in a shortened wording: