“Fi Amanillah” means “[May you be] in the protection of Allah.” It is a farewell — you entrust the one leaving to the best of guardians. The Qur'an calls Allah exactly that: the best of protectors.
“...But Allah is the best guardian, and He is the most merciful of the merciful.”— 12:64 (Saheeh International)
Ask Noor can share the Sunnah farewell duas and how to reply to Fi Amanillah.
Ask Noor — free on the App Store