بِسْـمِ اللَّـهِ وَالصَّلاةُ وَالسّلامُ عَلَى رَسُوْلِ اللَّـهِ
اللَّهُـمَّ إِنِّـي أَسْأَلُـكَ مِـنْ فَضْـلِكَ
اللَّهُـمَّ اعْصِمْنِـي مِنَ الشَّيْـطَانِ الرَّجِـيْم
Bismillahi, was-salatu was-salamu 'ala Rasulillah.
Allahumma inni as'aluka min fadlik,
Allahumma 'simni minash-shaytanir-rajim
Translation
In the name of Allah, and prayers and peace be upon the Messenger of Allah. O Allah, I ask You from Your favour. O Allah, guard me from the accursed devil
When to recite
Upon leaving the mosque.
Source / Reference
Hisnul Muslim 21