Muwatta Malik, Book 9, Hadith 372 (In-Book)

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 ‏.‏

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also referenced under: Book 9, Hadith 43 (USC-MSA)