مُوَطَّأُ مَالِكٍ
Muwatta Malik 397
Shortening the Prayer
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ أَبِي جَعْفَرٍ الْقَارِئِ، أَنَّهُ قَالَ كُنْتُ أُصَلِّي وَعَبْدُ اللَّهِ بْنُ عُمَرَ وَرَائِي وَلاَ أَشْعُرُ فَالْتَفَتُّ فَغَمَزَنِي .
Yahya related to me from Malik that Abu Jafar al-Qari said, "I was praying, and Abdullah ibn Umar was behind me and I was not aware of it. Then I turned round and he prodded me (in disapproval)."
Arabic/English book reference: Book 9, Hadith 66