Palestinian amora of the fourth generation (4th cent.); junior contemporary, and probably pupil, of Abbahu, in whose name he repeats several halakic decisions and homileticremarks (Yer. Dem. 23c; Pes. 29d; Pesiḳ, 75b; Sheb. 4:35a; Niddah 2:6a). He also repeats halakot in the names of Jeremiah and Jose II. (Kelim. 1:1).
Jacob was a firm believer in the powers of magic. Bread or other eatables found on the road must not be touched, according to him, because such food may have been laid there for magical purposes (Lev. R. ). From the words "And the people spake against God, and against Moses" (Numbers 21:5) Jacob infers that he who speaks against his teacher is as though he insulted the majesty of God (Midr. Teh. ).