the Messenger of Allah forbade selling surplus water. The keeper of al-Wahat sold the surplus water of al-Wahat, and ‘Abdullah bin ‘Arm disapproved of that.
That the Prophet (ﷺ) said: “Fulfill the trust for the one who entrusted you, and do not cheat the one who cheated you.” This Hadith is Hasan Gharib. Some of the people of knowledge followed this Hadith, they said that when something belonging to a man is with another and he leaves (with it), then he has something that belongs to him, he may not withhold from him an equivalent to what the other took of his. Some of the people of knowledge among the Tabi’in allowed that. This is the view of Sufyan Ath-Thawri, he said: “If one man has some Dirham that belong to another, and the second has some Dinar belonging to the first, he may not withhold any in place of his Dirham, unless it so happens that he has some Dirham of his, then in that case he can withhold some of his Dirham equal to what he is owed by the first.”