Jabir told that a slave came and swore allegiance to the Prophet promising to emigrate, but he did not know that he was a slave. When his master came in search of him the Prophet said to him, ‘Sell him to me," and he bought him for two black slaves. Afterwards he never took an oath of allegiance from anyone without asking him whether he was a slave or free.
Fadala b. 'Ubaid* said that at the battle for Khaibar he had bought a necklace in which there were gold and gems for twelve dinars, and after considering them separately he found that it was worth more than twelve dinars, so he mentioned that to the Prophet who said, "It must not be sold till the contents are considered separately."
Muslim transmitted it.
* The Damascus edition, iii, 308 and Mirqat, iii, 311 wrongly give Abu 'Ubaid, but in the commentary Mirqat gives the name correctly as Fadala b. 'Ubaid.
Abu Sa'id said that Bilal brought the Prophet some barni* dates, and when he asked him where he had got them he replied, "I had some inferior dates, so I sold two sa's of them for a sa." He said, "Ah, the very essence of usury, the very essence of usury. Do not do so, but when you wish to buy, sell the dates in a separate transaction, then buy with what you get."
(Bukhari and Muslim.)
* A type of dates of the best quality, sweet and luscious, red tinged with yellow.