Muwatta Malik, Book 18, Hadith 15 (USC-MSA)

Yahya related to me from Malik from Yahya ibn Said that Atika bint Zayd ibn Amr ibn Nufayl, the wife of Umar ibn al-Khattab, used to kiss Umar ibn al-Khattab's head while he was fasting, and he did not tell her not to.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّ عَاتِكَةَ ابْنَةَ زَيْدِ بْنِ عَمْرِو بْنِ نُفَيْلٍ، - امْرَأَةَ عُمَرَ بْنِ الْخَطَّابِ - كَانَتْ تُقَبِّلُ رَأْسَ عُمَرَ بْنِ الْخَطَّابِ وَهُوَ صَائِمٌ فَلاَ يَنْهَاهَا ‏.‏

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also referenced under: Book 18, Hadith 648 (In-Book)