Muwatta Imam Malik Book of Shortening the Prayer, Hadith 43

Yahya related to me from Malik that he had heard that Ali ibn Abi Talib said, "Things that pass in front of a man praying do not break his prayer."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ، قَالَ لاَ يَقْطَعُ الصَّلاَةَ شَىْءٌ مِمَّا يَمُرُّ بَيْنَ يَدَىِ الْمُصَلِّي .