Midrasch zu Wajikra 6:14

1) (Vayikra 6:14) ("On a griddle with oil, shall it be made; soaked shall you bring it; well-baked, a meal-offering of pieces shall you offer it, a sweet savor to the L–rd.") "On a griddle": We are hereby taught that it is a (ministering) vessel. "with oil": Oil is to be added to it (above the amount for the griddle offering of an Israelite). I would not know how much (oil to use). I, therefore, induce: This requires oil and the libation meal-offering (Shemoth 29:40) requires oil. Just as the libation meal-offering (requires) three logs for the issaron (viz. Shemoth 29:40), this, too, requires three logs for the issaron.

2) But why not go in this direction: This requires oil and a gift meal-offering requires oil. Just as a gift meal-offering requires one log for the issaron, this, too, requires one log for the issaron!

3) Let us see what it most closely resembles. We derive it from a meal-offering (the libation meal-offering) which is offered always (every day, with the tamid offering) and which overrides Shabbath and tumah, and not from a gift meal-offering, which lacks these factors.