Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever lets a Muslim cancel a sale, Allah Almighty will forgive his slip too." And in the narration of al-Misri the words are: "Whoever lets a remorseful person cancel his sale, Allah Almighty will also forgive him his slip." [Abu Dawud, hadith: 3460, Ibn Majah: 2199]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11128