Muwatta Malik, Book 18, Hadith 26 (USC-MSA)

Yahya related to me from Malik that Hisham ibn Urwa said, "My father, Urwa, used to travel in Ramadan, and we would travel with him, and he used to fast while we would break the fast, and he would not tell us to fast."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّهُ كَانَ يُسَافِرُ فِي رَمَضَانَ وَنُسَافِرُ مَعَهُ فَيَصُومُ عُرْوَةُ وَنُفْطِرُ نَحْنُ فَلاَ يَأْمُرُنَا بِالصِّيَامِ ‏.‏

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also referenced under: Book 18, Hadith 660 (In-Book)