And this is one of the ten things created on Sabbath eve (of the creation) at twilight: the rainbow, the manna, the staff (with which the signs were performed), the writing, (the form of the letters carved on the tablets), the shamir (a miraculous stone-cutting worm), the tablets, the opening of the mouth of the earth to swallow up the wicked, the opening of the mouth of (Bilam's) ass, the grave of Moses, and the cave where Moses and Eliyahu stood. Others say: Also the vestments of the first man and the staff of Aaron, its almonds and blossoms.
This Is One of the Ten Things Created on Sabbath Eve
Mekhilta Tractate Vayassa 6:12