Majma al-Zawaid — Hadith 4715

Abu Salamah Bishr bin Bashir al-Aslami narrates from his father: When the Muhajirun came to Madinah, its water did not suit them. A man from Banu Ghifar had a well called Rumah, and he used to sell a waterskin of it for a mudd. The Prophet (peace and blessings be upon him) said to him: "Sell it to me in exchange for a well in Paradise." He said: "O Messenger of Allah! I and my family have no other source of income besides it; I cannot do that." When Sayyiduna Uthman (may Allah be pleased with him) learned of this, he bought it for thirty-five thousand dirhams. Then he came to the Prophet (peace and blessings be upon him) and said: "O Messenger of Allah! Will you make me the same offer you made to that man, that I will get a well in Paradise if I buy this well?" The Prophet (peace and blessings be upon him) said: "Yes." He said: "I have bought it, and I dedicate it to the Muslims."
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain contains a narrator, Abd al-A'la bin Abi al-Musawir, and he is da'if (weak).