Muwatta Malik, Book 31, Hadith 1352 (In-Book)

Yahya related to me from Malik from Nafi that Abdullah ibn Umar bought a female riding-camel for four camels and he guaranteed to give them in full to the buyer at ar-Rabadha.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، اشْتَرَى رَاحِلَةً بِأَرْبَعَةِ أَبْعِرَةٍ مَضْمُونَةٍ عَلَيْهِ يُوفِيهَا صَاحِبَهَا بِالرَّبَذَةِ ‏.‏

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also referenced under: Book 31, Hadith 60 (USC-MSA)