[If] someone sells his field, the seller is permitted, but the buyer is forbidden.  A person may not hire workers on condition that his son shall glean behind him. [If] one does not allow the poor to glean, or [if] he allows one and not another, or [if] he assists one of them, he is robbing the poor. About this it is said: Move not the landmark of them that came up (Proverbs 22:28; 23:10).