Accompanying a Jew at the beginning of their journey is a Mitzvah. It guarantees that no harm will befall them as they go. Yet as a result of Pharoh walking 4 steps to escort Avrohom, the Jews become enslaved for 400 years in Egypt.

Sources:

Bereishis Vayeshev Perek 37 Possuk 14.

Commentery of Rashi and Baal Haturim

Bereishis Vayechi Perek 50 Possuk 7

Commentery of Baal Haturim

Gemara Sotah 46 B

End of Tosafos Sotah 42 B ‘Meah Popei’

Bartenura begining of Pirkei Avos