The Book of Mosques and Places of Prayer
5/30. Chapter:
The one who catches up with a rak`ah of the prayer, he has caught up with that prayer
Sahih Muslim
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.
Reference : Sahih Muslim 608dIn-book reference : Book 5, Hadith 212USC-MSA web (English) reference : Book 4, Hadith 1267