The Book of Mosques and Places of Prayer
وَحَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا ابْنُ إِدْرِيسَ، عَنِ الْحَسَنِ بْنِ عُبَيْدِ اللَّهِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، أَنَّهُ صَلَّى بِهِمْ خَمْسًا .Alqama reported:He (the Holy Prophet) had led them five rak'ahs in prayer
From Sahih Muslim, whose reports the scholars accept as authentic.