al-Qasim ibn Muhammad القاسم بن محمد بن أبي بكر الصديق · Wages (Kitab Al-Ijarah)

They (the people) used to buy grain in the upper part of the market in the same spot without measuring or weighing it. The Messenger of Allah (ﷺ) forbade them to sell it there before removing it.

The Prophet (ﷺ) said: The similitude of the one who takes back what he gifted is like that of a dog which vomits and then it eats vomit. When a donor seeks to take back (his gift), it should be made known and he informed why he sought to take it back. Then whatever he donated should be returned to him.