פירוש על קידושין 34:2

According to the first opinion, even if the master’s house has not prospered while the slave was serving, the master must still grant him a gift. If the house was blessed, the master should (but not must) give him more. If the house was not blessed, there is still a minimal amount.
R. Elazar b. Azariah says the master must give him only if the house was blessed. R. Elazar ben Azariah does not read anything into the word “you shall grant him.” This is simply the only way the Torah could express the idea that if the house was blessed on his behalf, the master should grant him a gift.