Where does “саха́” come from?

саха́ (Russian) comes from Yakut саха, from Proto-Turkic jaka — collar; edge; edge; collar; collar.

Ancestry of “саха́”, step by step

Step	Language	Word	Meaning
1	Yakut	саха	Sakha, Yakuts
2	Proto-Turkic	jaka	collar; edge; edge; collar; collar