Nittai of Arbela (Hebrew: נתאי הארבלי) was av beit din or vice-president of the Sanhedrin under the nasi Joshua ben Perachyah at the time of John Hyrcanus (r. 134–104 BC).
The confusion in the rendering of his name seems to be due to faulty textual transmission, i.e. the Hebrew mem being separated graphically into two parts, which looked, respectively as a nun and a yod, thus Mattai became Nittai.
No halakhot of his are extant, but some of his apothegms have been preserved in such sources as Pirkei Avot; these afford a glimpse of his character, to wit: "Distance thyself from a bad neighbor; consort not with an evil man, nor despair at tribulation.
Nittai seems to have spoken thus after John Hyrcanus had deserted the party of the Pharisees and joined the Sadducees, persecuting his former friends.
The phrase "renounce not the hope of retribution" was perhaps intended to comfort the Pharisees with the thought that Hyrcanus himself would not escape punishment, while the other two injunctions were designed maybe to keep them from joining the Sadducees.