[Ruling on taking soil or gravel from private irrigation channels]

Answer: The criterion is custom. If the custom among the people of that town is to be lenient about taking gravel or soil from their private rights, or about taking a certain amount thereof, then taking soil or gravel is permissible according to the custom. If the custom is that such lenience is not granted, then it is not permissible to take anything except with the right-holder’s permission.
If the man took without permission, then what is incumbent upon him is to seek their pardon and good pleasure. The apparent position of the madhhab is that he need not pay the value of what he took—because what was taken is a right, not full ownership, and rights are not bought and sold. If the taker removed soil in a way that caused harm, he must repair what he damaged.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2