Midrash Tanchuma, Beshalach 4/מדרש תנחומא·בשלח ד׳

1And the Lord went before them (Exod. 13:21). Just as a man treats other men, so is he treated. Because Abraham escorted the ministering angels, as it is said: And Abraham went with them to bring them on the way (Gen. 18:16), the Holy One, blessed be He, accompanied his sons in the wilderness for forty years. And because Abraham said: Let now a little water be fetched (ibid., v. 4), as is written in the portion And He appeared unto him (Gen. 18:1), the Holy One, blessed be He, caused the well to appear for his children.