Lev 19:9-10 - Don't glean to the edges
This is a very powerful principle that all people should live by. Whenever God provides for us He often times gives enough to spare, and the principle to follow is that you should allow the spare to remain for the poor. It's not that you should "only" give the spare, but that you never need to collect the spare. You can and should still give sacrificially and abundantly, but the principle that you live your life by and that you run your business by should be that whenever there's extra I give that to the poor.
It's like when you go out to eat - you don't finish your plate and then you ask for a to-go box. They box it up and ask you're walking to your car you see a homeless guy. Boom, right there you have an opportunity to not glean to the edge of your field. Or you buy a new phone and you can get $100 on a trade-in for your old phone, but you decide that you'll just give the old one away to someone who can't afford a new phone simply because $100 to you is far less valuable than $100 to him. This is not gleaning to the edge of your field.
Here's what Matthew Henry says:
"That they should leave the gleanings of their harvest and vintage for the poor,v. 9,v. 10. Note, Works of piety must be always attended with works of charity, according as our ability is. When they gathered in their corn, they must leave some standing in the corner of the field; the Jewish doctors say, "It should be a sixtieth part of the field;’’ and they must also leave the gleanings and the small clusters of their grapes, which at first were overlooked. This law, though not binding now in the letter of it, yet teaches us, 1. That we must not be covetous and griping, and greedy of every thing we can lay any claim to; nor insist upon our right in things small and trivial. That we must be well pleased to see the poor supplied and refreshed with the fruit of our labours. We must not think every thing lost that goes beside ourselves, nor any thing wasted that goes to the poor. 3. That times of joy, such as harvest-time is, are proper times for charity; that, when we rejoice, the poor may rejoice with us, and when our hearts are blessing God their loins may bless us."