مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 704
Prayer
Mosques and places of Prayer - Section 1
وَعَنْ أَبِي قَتَادَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «إِذَا دَخَلَ أَحَدُكُمُ الْمَسْجِدَ فَلْيَرْكَعْ رَكْعَتَيْنِ قَبْلَ أَنْ يجلس»
Abu Qatada reported God’s Messenger as saying, “When one of you enters the mosque he should pray two rak'as before sitting down.” (Bukhari and Muslim.)
Mishkat al-Masabih, 704مُتَّفَقٌ عَلَيْهِ (الألباني)