Rashi on Exodus 4:20/רש"י על שמות ד׳:כ׳

1על החמור UPON “THE” ASS — the ass designated for this purpose: this was the ass which Abraham had saddled for the purpose of travelling to bind Isaac on Mount Moriah, and this, too, is the ass upon which King Messiah will once show himself in public, as it is said, (Zechariah 9:9) “[Behold, thy king cometh unto thee, …] lowly and riding upon an ass” (Pirkei DeRabbi Eliezer 31).

2וישב ארצה מצרים ויקח משה את מטה AND HE RETURNED TO THE LAND OF EGYPT: AND MOSES TOOK THE STAFF [OF GOD] — “Earlier and later” are not strictly observed in the Scriptures (i. e. incidents are not necessarily related in the exact order in which they occur. Here it should state: He took the staff etc. and returned to Egypt; cf. v. 17).