مُوَطَّأُ مَالِكٍ
Muwatta Malik 304
Prayer in Congregation
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّهُ قَالَ قُمْتُ وَرَاءَ عَبْدِ اللَّهِ بْنِ عُمَرَ فِي صَلاَةٍ مِنَ الصَّلَوَاتِ وَلَيْسَ مَعَهُ أَحَدٌ غَيْرِي فَخَالَفَ عَبْدُ اللَّهِ بِيَدِهِ فَجَعَلَنِي حِذَاءَهُ .
Yahya related to me from Malik that Nafi said, "I stood behind Abdullah ibn Umar in one of the prayers when there was no one else with him, and he reached behind with his hand and placed me beside him."
Arabic/English book reference: Book 8, Hadith 15