Reference for Keritot 48:8

כי סליק נפשיה מדין ודברים מגופה דשדה לא סליק נפשיה

Now according to R'Simeon B'Gamaliel it is well, for he argues: When a man bestows a gift it is with the understanding that it be accepted; and if it is not accepted, it [automatically] returns to its original owner.

Jastrow