Does a person drink from a well and throw a stone into it?!
Figuratively: Is such ingratitude possible?! It is not typical for a person to harm someone who has brought him benefit.
("And he said to him (God, the Blessed One, to Moses): Where are the Egyptians drinking? He said to him: From Nile. He said to him: Turn it into blood. He said to him: I am not able to turn it, is there a man who drinks from the well, throwing a stone into it?! (Moses was saved by the merit of the ark that ruled over the river)" - Shemot Rava 20)
Translation
Expression (Hebrew)
יֵשׁ אָדָם שׁוֹתֶה מִן הַבְּאֵר וּמַשְׁלִיךְ אֶבֶן לְתוֹכָהּ?!
Definition (Hebrew)
בְּהַשְׁאָלָה: הַאִם תִּתָּכֵן כְּפִיּוּת טוֹבָה שֶׁכָּזֹאת?!, אֵין זֶה אָופְיָינִי לְהִתְנַהֲגוּתוֹ שֶׁל אָדָם לְהַזִּיק לְמִי שֶׁהֵבִיא לוֹ תּוֹעֶלֶת.
("אָמַר לוֹ (הקב"ה לְמֹשֶׁה): הֵיכָן מִצְרַיִם שׁוֹתִים?אָמַר לוֹ: מִנִּילוּס. אָמַר לוֹ: הֲפֹךְ אוֹתוֹ לְדָם. אָמַר לוֹ: אֵינִי יָכוֹל לְהָפְכוֹ, יֵשׁ אָדָם שׁוֹתֶה מִן הַבְּאֵר מַשְׁלִיךְ אֶבֶן לְתוֹכָהּ?! (מֹשֶׁה נִצַּל בִּזְכוּת הַתֵּבָה שֶׁשָּׁטָה עַל הַיְּאוֹר)"- שְׁמוֹת רַבָּה כ)