Abu Uthman narrates from Sayyiduna Salman (may Allah be pleased with him) that he said: I made a contract of manumission (mukatabah) with my masters on the condition that I would plant five hundred date saplings for them, and when they took (and bore fruit), I would be free. I came to the Prophet (peace and blessings be upon him) and mentioned this to him. He (peace and blessings be upon him) said: "Plant, and agree the condition with them, but when you intend to plant, inform me." I informed him (peace and blessings be upon him), and he came and began planting them, except for one which I planted with my own hand. All of them took (and bore fruit) except that one.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21624
Abdullah bin Buraydah (may Allah have mercy on him) narrates from his father (Sayyiduna Buraydah, may Allah be pleased with him) that when Sayyiduna Salman (may Allah be pleased with him) came to Madinah, he placed a gift on a platter before the Messenger of Allah (peace and blessings be upon him). He (peace and blessings be upon him) asked: "Salman, what is this?" He said: "It is charity (sadaqah) for you (peace and blessings be upon him) and your Companions (may Allah be pleased with them)." He (peace and blessings be upon him) said: "I do not eat charity." So he took it away. The next day he again placed something on a platter in the same way, and he (peace and blessings be upon him) asked: "What is this?" He said: "This is a gift for you (peace and blessings be upon him)." The Messenger of Allah (peace and blessings be upon him) said to his Companions (may Allah be pleased with them): "Eat." He (peace and blessings be upon him) asked: "To whom do you belong?" He said: I am the slave of a people. He (peace and blessings be upon him) said: "Ask them to make a contract of manumission (mukatabah) with you." He says: They made a contract with me that I would plant such-and-such a number of date palms for them, and that Salman would tend them until they bore fruit. They did so, and the Prophet (peace and blessings be upon him) planted all the palms except one, which Sayyiduna Umar (may Allah be pleased with him) planted. All the palms bore fruit within the year except that palm. The Messenger of Allah (peace and blessings be upon him) asked: "Who planted this?" They said: Sayyiduna Umar (may Allah be pleased with him). So he (peace and blessings be upon him) planted it again with his own blessed hand, and it too bore fruit that same year.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21625
Abdullah bin Abbas (may Allah be pleased with them both) says that Salman al-Farisi (may Allah be pleased with him) related the story of his accepting Islam. In it is that the Messenger of Allah (peace and blessings be upon him) said: "O Salman, make a contract of manumission (mukatabah)." So I made a contract with my masters to bring three hundred date palms to life and to pay forty uqiyahs. The Companions (may Allah be pleased with them) of the Messenger of Allah (peace and blessings be upon him) gave me (saplings), some 30, some 20, some 10, each according to his means. In another narration it is that the Prophet (peace and blessings be upon him) went out with me, and we were carrying the young palm shoots; he (peace and blessings be upon him) would take the shoot in his hand and set it level in the ground. By Allah, not a single shoot perished. The dirhams remained due from me, and a man brought gold the size of an egg. He (peace and blessings be upon him) said: "Where is the Persian Muslim mukatab?" I was called, and he (peace and blessings be upon him) said: "Salman, take this and pay off what you owe." I said: O Messenger of Allah, how will this pay off what I owe? He (peace and blessings be upon him) said: "Allah will pay it off for you by means of it." By the One in whose hand is the soul of Salman, I weighed out 40 uqiyahs from it for them and gave it to them, and Salman (may Allah be pleased with him) was freed.
The Shaykh says: In the first narration the number of trees is greater, and the condition is freedom, and one of the trees, which the Prophet (peace and blessings be upon him) had not planted, did not take; in the third narration the number of trees is smaller, with the addition of 40 uqiyahs; and in the second narration there is the condition of the trees bearing fruit. This was an agreement with the disbelievers for freedom, and the Messenger of Allah (peace and blessings be upon him) permitted making such a condition.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21626
Zayd bin Suhan says regarding the story of the Islam of Sayyiduna Salman (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) asked: "Whose slave are you?" I said: "Of a woman of the Ansar, who has put me to work in her garden." He (peace and blessings be upon him) said: "O Abu Bakr (may Allah be pleased with him)!" He said: "O Messenger of Allah, at your service." He (peace and blessings be upon him) said: "Buy him." So Sayyiduna Abu Bakr (may Allah be pleased with him) bought me and set me free.
Note: This narration differs from the earlier narrations. It is possible that he did not obtain his freedom because one tree did not bear fruit, so the Prophet (peace and blessings be upon him) replanted it with his own hand, and that in the meantime Abu Bakr (may Allah be pleased with him) bought him.
The authenticity of some of these narrations is open to question.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21627