A worshipper acting on the word of someone not in the prayer

Question

A man is a masbuq in the prayer, but he does not remember that he is a masbuq. When the imam gave the salam, he also gave it along with him. Another man was standing beside him; after the salam had been given, he reminded him: “You still have one rak'a remaining.” Taking the prompt (fath) from the one who prompted him, he completed the rak'a. Will the prayer of the one who was prompted be valid or not? Kindly write [the answer] with the texts [of the books] and references to the books and pages!

Answer

If he stood up [to complete the rak'a] solely because of the prompting of the one who prompted him, and did not remember by himself, the prayer became fasid (invalid): [ar]وفتحه على غير إمامه إلا إذا أراد التلاوة، وكذا الأخذ إلا إذا تذكر فتلا قبل تمام الفتح[/ar] “And [it invalidates the prayer] that he prompts someone other than his own imam — unless he intended [mere]…

Source: Fatawa Mahmudiyya

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