What is the Earliest Source? 3 - from Matzah to Hameitz

Traditionally speaking several Halachah s'farim have told us to hang on to things such the lulav - in order to use it as fuel with which to Bake Matzot.

Nowadays this has morphed into using lulavim and such as fuel with which to Burn Hameitz instead.

What is the earliest source to suggest this transition from using discarded lulavim for baking Matzot to burning Hameitz?

KT
RRW