From the way to Egypt, upon the occasion mentioned Exodus 4:24,25, and because he found by experience that she was likely to hinder him from, or discourage him in, the discharge of his great and dangerous office, and to give an ill example to the Israelites.
Related Commentaries of Exodus 18:2
Exodus 18:2
2 Then Jethro, Moses' father in law, took Zipporah, Moses' wife, after he had sent her back,