Muwatta Malik, Book 36, Hadith 5 (USC-MSA)

Yahya said, "Malik said from Jafar ibn Muhammad from his father that the Messenger of Allah, may Allah bless him and grant him peace, pronounced judgement on the basis of an oath with one witness."

قَالَ يَحْيَى قَالَ مَالِكٌ عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَضَى بِالْيَمِينِ مَعَ الشَّاهِدِ ‏.‏

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also referenced under: Book 36, Hadith 1409 (In-Book)