Two sales in one sale are not permitted, nor selling what one does not own, nor a loan combined with a sale, nor two conditions in one sale

It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) that he said: I said: "O Messenger of Allah, I hear things from you that I fear I will forget; do you permit me to write them down?" He (peace and blessings be upon him) said: "Yes." Among the things he wrote down from the Messenger of Allah (peace and blessings be upon him) was that when he (peace and blessings be upon him) sent Attab bin Asid (may Allah be pleased with him) to the people of Makkah (as governor), he (peace and blessings be upon him) said: "Inform them that two deals in one sale are not permissible, nor is the sale of what one does not own, nor combining a loan with a sale, nor two conditions in one sale."

It is narrated from Umarah bin Khuzaymah, from his paternal uncle (who was a Companion of the Messenger of Allah), that the Messenger of Allah (peace and blessings be upon him) bought a horse from a Bedouin. The Messenger of Allah (peace and blessings be upon him) took him along behind him in order to pay him the price of his horse. He (peace and blessings be upon him) walked quickly while the Bedouin lagged behind. Meanwhile, some people met the Bedouin and began bargaining with him over the horse, not knowing that the Messenger of Allah (peace and blessings be upon him) had already bought it, until some of them offered the Bedouin a higher price. When the price went up, the Bedouin called out: "O Messenger of Allah, if you are going to buy this horse then buy it; otherwise I am selling it." When the Messenger of Allah (peace and blessings be upon him) heard the Bedouin's call, he stood up, came to him and said: "Did I not buy it from you?" He said: "No, by Allah, I did not sell it to you." He (peace and blessings be upon him) said: "Indeed, I did buy it from you." The people gathered around the Messenger of Allah (peace and blessings be upon him) and the Bedouin while the two of them were disputing the matter. The Bedouin began saying: "Bring a witness that I sold it to you." Then Sayyiduna Khuzaymah (may Allah be pleased with him) said: "I bear witness that you (peace and blessings be upon him) bought it." The Messenger of Allah (peace and blessings be upon him) turned to Khuzaymah and asked: "On what basis do you bear witness?" He said: "On the basis of affirming you (as a Prophet)." So the Messenger of Allah (peace and blessings be upon him) made the testimony of Khuzaymah equal to the testimony of two men.
This hadith has a sahih (authentic) chain, and its narrators are trustworthy by the agreement of the two Shaykhs, but they did not record it.

It is narrated from Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) bought a horse from Sawa' bin al-Harith al-Muharibi, but he denied (having sold it). So Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) bore witness in his (peace and blessings be upon him) favour. The Messenger of Allah (peace and blessings be upon him) asked him: "What moved you to bear witness when you were not present?" He said: "O Messenger of Allah, you have spoken the truth; rather, I affirmed what you told us, and I know that you say nothing but the truth." Then he (peace and blessings be upon him) said: "Whoever Khuzaymah bears witness for or against, that is sufficient for him."

It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that he said: In the time of the Messenger of Allah (peace and blessings be upon him) and Sayyiduna Abu Bakr (may Allah be pleased with him) we used to sell ummahat al-awlad (slave women who had borne children to their masters), but when the time of Sayyiduna Umar (may Allah be pleased with him) came, he forbade us from it, so we stopped.
This hadith is sahih (authentic) on the condition of Muslim, but the two Shaykhs did not record it.

It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that he said: In the blessed time of the Messenger of Allah (peace and blessings be upon him), we used to buy and sell ummahat al-awlad.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Any slave woman who bears a child to her master is free after his death."
This hadith has a sahih (authentic) chain, but the two Shaykhs did not record it.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said concerning the mother of Ibrahim (his (peace and blessings be upon him) son, Sayyidah Mariyah al-Qibtiyyah) when he was born: "Her son has set her free."