It wasnarrated that Jabir said:
"A slave came and gave his pledge totheProphet (ﷺ), pledging to emigrate, and the Prophet (ﷺ) did notrealize that he was a slave. Then his master came looking for him,andthe Prophet (ﷺ) said: 'Sell him to me,' and he brought himinexchange for two black slaves. Then after that he did not acceptthepledge from anyone until he had asked whether he was a slave." (FR)
English reference (FR): Vol. 4, Book 24, Hadith 2869 (FR)
Arabic reference (FR): Book 24, Hadith 2979 (FR)