Muwatta Malik, Book 2, Hadith 97 (In-Book)

Yahya related to me from Malik that he had heard that Abdullah ibn Masud used to say, "Wudu is necessary if a man kisses his wife."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، كَانَ يَقُولُ مِنْ قُبْلَةِ الرَّجُلِ امْرَأَتَهُ الْوُضُوءُ ‏.‏

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also referenced under: Book 2, Hadith 67 (USC-MSA)