Sahih Muslim 608
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · The one who catches up with a rak`ah of the prayer, he has caught up with that prayer
وَحَدَّثَنَاهُ عَبْدُ الأَعْلَى بْنُ حَمَّادٍ ، حَدَّثَنَا مُعْتَمِرٌ ، قَالَ سَمِعْتُ مَعْمَرًا ، بِهَذَا الإِسْنَادِ .
This hadith has been reported by Ma'mar with another chain of transmitters.