Leviticus 19:9
"And when ye reap the harvest of your land, thou shalt not wholly reap the corners of thy field, neither shalt thou gather the gleanings of thy harvest."
Cross References (ranked by relevance)
And when ye reap the harvest of your land, thou shalt not make clean riddance of the corners of thy field when thou reapest, neither shalt thou gather any gleaning of thy harvest: thou shalt leave them unto the poor, and to the stranger: I am the LORD your God.
And when she was risen up to glean, Boaz commanded his young men, saying, Let her glean even among the sheaves, and reproach her not:
And Ruth the Moabitess said unto Naomi, Let me now go to the field, and glean ears of corn after him in whose sight I shall find grace. And she said unto her, Go, my daughter.
Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the firstfruits of your harvest unto the priest: