The Source of the Commandment to Eat on the Eve of Yom Kippur

What is the source for the statement that there is a commandment to eat on the eve of Yom Kippur?

Shalom and blessings,

The source for this is a drasha from the verse mentioned in the Gemara (Berachot 8:): 'Chiya bar Rav from Difti taught: it is written "and you shall afflict your souls on the ninth day of the month in the evening," do we fast on the ninth? Don't we fast on the tenth? Rather, this teaches us that whoever eats and drinks on the ninth, it is considered by the scripture as if he fasted on both the ninth and the tenth.' This means that the Gemara derives from the verse that there is a commandment to eat on the eve of Yom Kippur, and whoever does so is considered as if he fasted both on the eve of Yom Kippur and on Yom Kippur itself.

The Mishnah Berurah (Siman 604, Seif Katan 1) explains the drasha as follows: 'And from what is written "and you shall afflict" etc., on the ninth day of the month, it implies that they fast on the ninth, but in truth, Yom Kippur is only on the tenth day of the month, and the sages accepted that, on the contrary, there is a Torah commandment to eat on the eve of Yom Kippur, and the Holy One, blessed be He, wanted to give a reward for eating as if they fasted, because a commandment that involves suffering, as they said, "according to the suffering is the reward," if it had been written "on the ninth day of the month you shall eat," we would have had a reward only as for fulfilling a commandment through eating, and therefore the scripture changed and wrote the commandment of eating in the language of fasting, so that this eating would be considered before the Holy One, blessed be He, as if it were a fast, to give a reward as for fulfilling a commandment with the suffering of affliction. And a person should reduce his study on the eve of Yom Kippur in order to eat and drink.'

Berachot (8:), Shulchan Aruch (Siman 604, Seif 1), and Mishnah Berurah (there, Seif Katan 1).