Phinehas ben Jair (Hebrew: פנחס בן יאיר) was a Tanna of the 4th generation who lived, probably at Lydda, in the second half of the 2nd century. He was the son-in-law of Shimon bar Yochai and a fellow disciple of Judah I. He was more celebrated for piety than for learning, although his discussions with his son-in-law (Shab. 33b) evince great sagacity and a profound knowledge of tradition.
An aggadah gives the following illustration of Phinehas' scrupulous honesty: Once two men deposited with him two seahs (a quantity) of wheat. After a prolonged absence of the depositors Phinehas sowed the wheat and preserved the harvest. This he did for seven consecutive years, and when at last the men came to claim their deposit he returned them all the accumulated grain (Deut. R. iii.).
Phinehas is said never to have accepted an invitation to a meal and, after he had attained his majority, to have refused to eat at the table of his father. The reason given by him for this course of conduct was that there are two kinds of people: (1) those who are willing to be hospitable, but can not afford to be so, and (2) those who have the means but are not willing to extend hospitality to others (Hul. 7b). Judah I once invited him to a meal, and exceptionally he decided to accept the invitation; but on arriving at the house of the patriarch he noticed in the yard mules of a certain kind the use of which was forbidden by local custom on account of the danger in handling them. Thereupon he retraced his steps and did not return (Hul. l.c.).
Special weight was laid by Phinehas upon the prescriptions relating to ma'aser (tithes). This feature of Phinehas' piety is described hyperbolically in the Aggadah. The latter relates a story of a mule belonging to Phinehas which, having been stolen, was released after a couple of days on account of its refusal to eat food from which the tithe had not been taken (Gen. R. lx, 8; comp. Ab. R. N. viii., end). To Phinehas is attributed the abandonment by Judah I of his project to abolish the year of release (Yer. Demai i. 3; Ta'an. iii. 1).