When any of you enters the mosque, let him send peace upon the Prophet and say: Allāhumma iftahli abwāba rahmatik (O Allah, open for me the gates of Your mercy)

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (ﷺ) said: "When any of you enters the mosque, let him send peace upon the Prophet and say: Allāhumma iftahli abwāba rahmatik (O Allah, open for me the gates of Your mercy). And when he leaves, let him send peace upon the Prophet and say: Allāhumma i‘simni min ash-shaytān ar-rajīm (O Allah, protect me from the accursed devil)."

In another narration by Al-Hākim: "When he leaves, let him send peace upon the Prophet (ﷺ) and say: Allāhumma ajirni min ash-shaytān ar-rajīm (O Allah, save me from the accursed devil)."

The Prophet (ﷺ) guided the Muslim, when entering the mosque, to send peace and blessings upon the Prophet (ﷺ) by saying: Allāhumma salli wa sallim ‘ala Muhammad (O Allah, send Your blessings and peace upon Muhammad), and then to say: Allāhumma iftahli abwāba rahmatik (O Allah, open for me the gates of Your mercy). And when he leaves, he should send peace upon the Prophet and say: Allāhumma i‘simni min ash-shaytān ar-rajīm (O Allah, protect me from the accursed devil).

In another narration by Al-Hākim: And say: Allāhumma ajirni min ash-shaytān ar-rajīm (O Allah, save me from the accursed devil).