Parashas Shemos · Passuk 1:11
וַיָּשִׂ֤ימוּ עָלָיו֙ שָׂרֵ֣י מִסִּ֔ים לְמַ֥עַן עַנֹּת֖וֹ בְּסִבְלֹתָ֑ם וַיִּ֜בֶן עָרֵ֤י מִסְכְּנוֹת֙ לְפַרְעֹ֔ה אֶת־פִּתֹ֖ם וְאֶת־רַעַמְסֵֽס׃
They placed upon him taskmasters in order to afflict him with their burdens; and he built store-cities for Pharaoh — Pisom and Raamses.
Torah Temimah points to Sotah 11a (verified).
למען ענותו בסבלותם — למען ענותם מבעי ליה. אלא למען ענותו לפרעה בסבלותם של ישראל.
English: “In order to afflict him with their burdens” — it should have said “to afflict them.” Rather: in order to afflict Pharaoh with the burdens of Israel.
Custom — diyuk from singular object.
The oppression designed against Israel was already worded so that it would rebound upon Pharaoh.