Related for Taanit 41:20

A man who says: "Give a shekel from my estate to my sons per week", but they are appropriate to receive a sela (=2 shekalim), they give to them a sela [since his intention was to give them enough per week, a shekel was a random amount]. But if he said: "Give them only a shekel", they only give them a shekel [since he was more specific]. If he said: "If they die, others should inherit me", whether he said "Give..." or "Give only...", they only give them a shekel [since there are others who stand to lose out if the sons get more money per week from the estate]. Rabban Shimon ben Gamliel says: Meir used to say: A man who says, "Give a shekel per week to my sons" and they are appropriate to receive a sela, they give them a shekel, and for the rest they are supported from tzedakah; but Hakhamim say: They are fed [from the estate] until they use up the estate, but for anything beyond that, they are supported from tzedakah.