Where does “отхлебать” come from?

отхлебать (Russian) comes from Russian от-, from Proto-Slavic otъ-.

Ancestry of “отхлебать”, step by step

Step	Language	Word	Meaning
1	Russian	от-	away from
2	Proto-Slavic	otъ-	—

отхлебать — Etymology, Origin & Word History | Etymology Explorer