Ibn Majah

Narrated Abu lWadi: We fought one of our battle, and encamped at a certain place. One of our companions sold a horse for a slave. After that they remained there for the rest of day and night. When the next morning came, they prepared themselves for departure. The buyer of the horse began to saddle it, but the seller was ashamed (of the transaction). He went to the man (buyer) and asked him to annul the transaction. The man refused to hand it over (the horse) to him. He said: Abu Barzah, the companion of the Prophet ﷺ, is to decide between me and you. They went to Abu Barzah in the corner of the army. They related this story to him. He said: Do you agree that I make a decision between you on the basis of the decision of the Messenger of Allah ﷺ? The Messenger of Allah ﷺ said: Both parties in a business transaction have an option (right) to annul it so long as they have not separated. Hisham to Hassan said that Jamil said in his version: "I do not think that you separated. "