This hadith has been reported by Ma'mar with another chain of transmitters.
Sahih Muslim Book 5, Hadith 212
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The Messenger of Allah (ﷺ) said: He who finds (gets) a rak'ah of the afternoon (prayer) before the setting of the sun, he in fact gets (the full prayer), and he who gets a rak'ah of the morning (prayer) before the rising of the sun he in fact gets (the full prayer).
Sahih Muslim Book 5, Hadith 211 Next Hadith → 'Umar b. 'Abd al-'Aziz deferred the afternoon prayer somewhat and 'Urwa said to him: Gabriel came down and he led the Messenger of Allah (ﷺ) in prayer. 'Umar said to him: O 'Urwa, are you aware of what you are saying? Upon this he ('Urwa) said: I heard Bashir b. Abu Mas'ud say that he heard Abu Mas'ud say that he heard the Messenger of Allah (ﷺ) say: Gabriel came down and acted as my Imam, then I prayed with him, then I prayed with him, then I prayed with him. then I prayed with him. then I prayed with him. reckoning with his fingers five times of prayer.
Sahih Muslim Book 5, Hadith 213
Sahih Muslim Book 5, Hadith 211 Next Hadith → 'Umar b. 'Abd al-'Aziz deferred the afternoon prayer somewhat and 'Urwa said to him: Gabriel came down and he led the Messenger of Allah (ﷺ) in prayer. 'Umar said to him: O 'Urwa, are you aware of what you are saying? Upon this he ('Urwa) said: I heard Bashir b. Abu Mas'ud say that he heard Abu Mas'ud say that he heard the Messenger of Allah (ﷺ) say: Gabriel came down and acted as my Imam, then I prayed with him, then I prayed with him, then I prayed with him. then I prayed with him. then I prayed with him. reckoning with his fingers five times of prayer.
Sahih Muslim Book 5, Hadith 213