TT #315 · Parashas Reeh · Sixth Aliyah · Passuk 15:14
You shall surely furnish him liberally from your flock and from your threshing floor and from your winepress; of that with which Hashem your God has blessed you, you shall give to him.
Torah Temimah points to Kiddushin.
English: "You shall surely furnish" — One might have thought that only if the household was blessed on his account do we furnish him, and if it was not blessed we do not; therefore the verse says "you shall surely furnish"—in every case. If so, what is the force of "with which Hashem has blessed you"? Give him according to the blessing.
Derash on the verse (Kiddushin) — the grant is always required, its size varies with the blessing.
One must always give a parting grant to a departing Hebrew slave; the amount is determined by the degree of blessing the master received.