مُوَطَّأُ مَالِكٍ
Muwatta Malik 181
Prayer
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَزِيدَ بْنِ رُومَانَ، أَنَّهُ قَالَ كُنْتُ أُصَلِّي إِلَى جَانِبِ نَافِعِ بْنِ جُبَيْرِ بْنِ مُطْعِمٍ فَيَغْمِزُنِي فَأَفْتَحُ عَلَيْهِ وَنَحْنُ نُصَلِّي .
Yahya related to me from Malik that Yazid ibn Ruman said, "I used to pray next to Nafi ibn Jubayr ibn Mutim and he would nudge me to prompt him while we were praying."
Arabic/English book reference: Book 3, Hadith 34