Halakha Ulangan 12:19: Mishneh Torah, Negative Mitzvot & Sefer HaChinukh

Not to forsake the Levites, as it is said, “Take heed to thyself that thou forsake not the Levite” (Deut. 12:19); but their gifts (dues) should be given to them, so that they might rejoice therewith on each and every festival.

Not to demand from a poor man repayment of his debt, when the creditor knows that he is poor, nor press him, as it is said, “Thou shalt not be unto him as a usurer” (Ex. 22:24).

To not forsake the Levite, from giving him his gifts: That we have been warned from forsaking the Levites and not to be negligent from filling their portion — meaning to say to not delay their tithes — and all the more so on festivals, as we are warned about them even more, in order to gladden them at the appointed time. And about this is it stated (Deuteronomy 12:19), “Be careful for yourself, lest you forsake the Levite, all of your days upon your Land.”