וַיַּשְׁכֵּ֨ם יַעֲקֹ֜ב בַּבֹּ֗קֶר וַיִּקַּ֤ח אֶת־הָאֶ֙בֶן֙ אֲשֶׁר־שָׂ֣ם מְרַֽאֲשֹׁתָ֔יו וַיָּ֥שֶׂם אֹתָ֖הּ מַצֵּבָ֑ה וַיִּצֹ֥ק שֶׁ֖מֶן עַל־רֹאשָֽׁהּ׃
Pri HaAretz
It is written in the Midrash "Taking one of the stones of that place", in the beginning there were many stones and for Jacob they became one stone. And it is therefore said "[Jacob] took the stone" (see there).