Where does “достоканъ” come from?

достоканъ (Old East Slavic) comes from Old Turkic dostaqan, from Persian dustgân, from Persian dôst.

Ancestry of “достоканъ”, step by step

Step	Language	Word	Meaning
1	Old Turkic	dostaqan	—
2	Persian	dustgân	—
3	Persian	dôst	—