From Torah Law, I need only put tzitzis on my own four-cornered garment. From Rabbinic Law, I need to attach tzitzis to a borrowed garment only after 30 consecutive days, see Oruch HaShulchan, O Ch 14 (8) .
What are the sources that deal with the law in the following (theoretical) case:
I borrowed a garment and attached tzitzis before 30 days. Later (a) within the 30 days or (b) after the 30 days, I acquired the garment from the owner.
Am I obliged to remove the tzitzis because they were only attached to fulfill a rabbinic law or did the Rabbis give their mitzva the force of a Biblical law and the tzitzis can be left in place.