Midrash su Numeri 29:38

(Exodus 12:2) "This month shall be to you the beginning of months": R. Yishmael says: Moses pointed out the new moon to Israel and said to them: Thus shall it (the moon) look and the new month be designated thereby for all generations. R. Akiva says: This is one of the three things which Moses could not visualize until they were pointed out to him by the L rd. Likewise, (Leviticus 11:29) "And this shall be unclean for you from among all the things that swarm upon the earth." (Likewise,) (Numbers 8:4) "And this is the work of the menorah." Others say: He was likewise perplexed as to slaughtering, viz. (Numbers 29:38) "And this is what you shall do upon the altar." R. Shimon b. Yochai says: Were not all of the mitzvoth spoken to Moses in the daytime? How, then, could he have pointed out the moon? R. Elazar says: He spoke with him just before it got dark and showed it to him when it got dark.