The seller stipulating the service of the sold slave for a known period

It is narrated from Sayyiduna Buraydah (may Allah be pleased with him) that when Sayyiduna Salman al-Farisi (may Allah be pleased with him) came to Madinah, he came to the Messenger of Allah (peace and blessings be upon him) with a gift on a platter and placed it before him. He (peace and blessings be upon him) asked: "O Salman, what is this?" He said: "It is charity for you and your Companions." He (peace and blessings be upon him) said: "I do not eat charity." So it was taken away. Then the next day he brought the same (platter) and placed it before him. He (peace and blessings be upon him) asked: "What is this?" He said: "It is a gift for you." Then the Messenger of Allah (peace and blessings be upon him) said to his Companions: "Eat as well." Then he (peace and blessings be upon him) asked: "To whom do you belong (as a slave)?" He said: "To such-and-such people." He (peace and blessings be upon him) said: "Ask them to make a contract of kitabah (an agreement for freedom) with you." Salman (may Allah be pleased with him) said: So they made a contract of kitabah with me in return for planting such-and-such a number of date palms, which Salman would tend until they bore fruit. The narrator said: So they did so. Then the Prophet (peace and blessings be upon him) came and planted all the date palms with his own hand except one tree; that one tree was planted by Sayyiduna Umar (may Allah be pleased with him). The trees he (peace and blessings be upon him) had planted bore fruit that same year, except that one tree. The Messenger of Allah (peace and blessings be upon him) asked: "Who planted this one?" The people said: "Umar (may Allah be pleased with him)." So the Messenger of Allah (peace and blessings be upon him) planted it (again) with his blessed hand, and it too bore fruit that same year.
This hadith is sahih (authentic) on the condition of Muslim, and Imam Abu Bakr (al-Bayhaqi) has recorded it in the chapter on the permissibility of the seller stipulating the service of the sold (slave) for a fixed period of time.

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that Sayyiduna Salman al-Farisi (may Allah be pleased with him) told me: A Jewish man bought him and brought him to Madinah. He said: Then I came to the Messenger of Allah (peace and blessings be upon him) with a gift and said: "This is charity." So he (peace and blessings be upon him) said to his Companions: "All of you eat," but he (peace and blessings be upon him) himself did not eat of it. Then he mentioned the rest of the hadith in the same way.
This supporting narration (shahid) is also sahih (authentic) on the condition of Muslim.

It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "It is not lawful to combine a loan with a sale, nor to stipulate two conditions in one sale, nor to take profit on something for which you bear no liability (for loss), nor to sell what you do not have (in your possession)."
This hadith is sahih (authentic) on the condition of a group of the Imams of the Muslims, and it has likewise been narrated from Amr bin Shu'ayb by Dawud bin Abi Hind, Abd al-Malik bin Abi Sulayman and others.