Where does “сутра” come from?

сутра (Russian) comes from Sanskrit सूत्र, from Proto-Indo-European *syewH-.

сутра (Russian): sutra

Definitions

Step	Language	Word	Meaning
1	Sanskrit	सूत्र	thread, yarn, string, line, cord, wire; a...
2	Proto-Indo-European	*syewH-	—

сутра — Etymology, Origin & Word History | Etymology Explorer