Sifrei_mitzvot for Deuteronomy 32:37

וְאָמַ֖ר אֵ֣י אֱלֹהֵ֑ימוֹ צ֖וּר חָסָ֥יוּ בֽוֹ׃

And it is said: Where are their gods, The rock in whom they trusted;