Deuteronomy 24:19
17 You must not pervert justice due a resident foreigner or an orphan, or take a widow’s garment as security for a loan. 18 Remember that you were slaves in Egypt and that the Lord your God redeemed you from there; therefore I am commanding you to do all this. 19 Whenever you reap your harvest in your field and leave some unraked grain there, you must not return to get it; it should go to the resident foreigner, orphan, and widow so that the Lord your God may bless all the work you do. 20 When you beat your olive tree you must not repeat the procedure; the remaining olives belong to the resident foreigner, orphan, and widow. 21 When you gather the grapes of your vineyard you must not do so a second time; they should go to the resident foreigner, orphan, and widow.
Ruth 2:10
8 So Boaz said to Ruth, “Listen carefully, my dear! Do not leave to gather grain in another field. You need not go beyond the limits of this field. You may go along beside my female workers. 9 Take note of the field where the men are harvesting and follow behind with the female workers. I will tell the men to leave you alone. When you are thirsty, you may go to the water jars and drink some of the water the servants draw.” 10 Ruth knelt before him with her forehead to the ground and said to him, “Why are you so kind and so attentive to me, even though I am a foreigner?” 11 Boaz replied to her, “I have been given a full report of all that you have done for your mother-in-law following the death of your husband—how you left your father and your mother, as well as your homeland, and came to live among people you did not know previously. 12 May the Lord reward your efforts! May your acts of kindness be repaid fully by the Lord God of Israel, from whom you have sought protection.”
Notes and References
"... This verse continues Boaz’ final set of instructions to his workers concerning Ruth. The fact that he not only allows Ruth to collect grain by following his harvesters through the field (instead of waiting until the harvest is finished) but also has his harvesters intentionally leave bundles for her goes well beyond the requirements of gleaning as it is described in Leviticus 19:9-10; 23:22; Deuteronomy 24:19-21. Leviticus 19 and 23 indicate that the “corner of the field” is to be left for those who need to glean, while Deuteronomy 24 suggests that forgotten or missed sheaves are to be left for the gleaners. In neither case, though, is the owner or harvesters instructed to intentionally leave behind sheaves from the harvest. Yet, this is precisely what Boaz is doing for Ruth ..."
Holmstedt, Robert D. Ruth: A Handbook on the Hebrew Text (p. 135) Baylor University Press, 2010