פירוש על קידושין 39:13

Abaye is walking down the streets feeling like a great scholar, in the grand old city of Tiberias, when some rabbis come up to him with the question I presented above.
Abaye responds that the Torah is lenient with the Hebrew slave. And if the Torah is lenient when it comes to the slave’s comforts, it clearly wishes us to be lenient when it comes to his redemption. Therefore he is always redeemed for the lower amount.