Muwatta Malik #76
Purity
The Arabic includes the chain of narration (sanad) and the collector's commentary; the English translation shows the Prophet's words only.
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، أَنَّهُ رَأَى أَبَاهُ يَمْسَحُ عَلَى الْخُفَّيْنِ قَالَ وَكَانَ لاَ يَزِيدُ إِذَا مَسَحَ عَلَى الْخُفَّيْنِ عَلَى أَنْ يَمْسَحَ ظُهُورَهُمَا وَلاَ يَمْسَحُ بُطُونَهُمَا .
Yahya related to me from Malik from Hisham ibn Urwa that he saw
his father wiping over his leather socks. He said, "When he wiped over
his socks he would never do more than wipe the tops and he would not
wipe the bottoms."
About Muwatta Malik
This hadith is #76 from Muwatta Malik, in the Book of Purity.