37 Bava Metzia 7/4-7

(4) If one was working with figs, he may not eat grapes; if with grapes, he may not eat figs; but he may restrain himself until he reaches the location of the best produce, and then eat. Concerning all of them, they only permitted so during the time of his labor. Because it is tantamount to returning lost property to its owner, they said: laborers may eat as they go from furrow to furrow, or as they return from the winepress, and a donkey while it is unloading.

(5) A laborer may eat cucumbers even up to [the value] of a dinar, and dates even up to [the value] of a dinar. Rabbi Elazar ben Khisma says: A laborer may not eat more than the value of his wage. The Sages permit it, but [we] teach a person not be gluttonous, [for he would] thus be closing the door upon himself.

(6) A person may stipulate for himself, and for his son or daughter who are adults, and for his adult male slave or adult female slave, and for his wife, because these have comprehension. But he may not stipulate for his son and daughter who are minors, or for his minor male slave or minor female slave or for his cattle, because these do not have comprehension.

(7) The one who hires laborers to work among his fourth-year plantings, they may not eat from them. If he had not informed them, he should redeem and then let them eat. If his fig-cakes were split or his jugs were opened, they may not eat from them. If he had not informed them, he should tithe and then let them eat.