Mishkat al-MasabihChapter 4Hadith 655
Full Sharh — Mishkat al-Masabih 655
وَعَنْ أَبِي أُسَيْدٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: " إِذَا دَخَلَ أَحَدُكُمُ الْمَسْجِدَ فَلْيَقُلِ: اللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ. وَإِذَا خَرَجَ فَلْيَقُلِ: الله إِنِّي أَسأَلك من فضلك ". رَوَاهُ مُسلم
English Translation
Abu Usaid reported God's Messenger as saying:: When any of you enters the mosque he should say, “O God, open to me the gates of Thy mercy, “and when he goes out he should say “O God, I ask Thee out of Thine abundance.” Muslim transmitted it.
Source
Mishkat al-Masabih(مشكاة المصابيح)
Prayer
Hadith Number
655