Rashi on Genesis 26:15/רש"י על בראשית כ״ו:ט״ו

1סתמום פלשתים THE PHILISTINES STOPPED THEM, saying, “They may become a source of danger to us because of marauding troops that may invade us” (i.e.,they may invade our country to obtain possession of the wells, or if they invade us for any other reason they will be able to find a supply of water). (Tosafot Sotah 10.) The rendering of the Targum טמונין means “stopping up” and we find it in the language of the Talmud (Pesachim 42a) “Chokes up (מטמטם) the heart”.