Dua for Leaving the Mosque
اللَّهُمَّ إِنِّي أَسْأَلُكَ مِنْ فَضْلِكَ
Allahumma inni as'aluka min fadlik.
"O Allah, I ask You from Your bounty."
Sahih Muslim 713
Spiritual Benefits
While you ask for 'mercy' when entering the mosque (spiritual focus), you ask for 'bounty' when leaving, acknowledging you are returning to the world to seek your halal livelihood.
When Should I Say This Dua?
Say this immediately as you step out of the mosque.
Proper Etiquette (Sunnah)
It is Sunnah to exit the mosque with your left foot first.