Sahih Muslim 714
Sahih Muslim · Book 6: The Book of Prayer - Travellers · It is recommended to greet the masjid by praying two rak`ah, and it is disliked to sit before praying these two rak`ah, and this is prescribed at all times
Abu Qatada, a Companion of the Messenger of Allah (ﷺ), said:
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا حُسَيْنُ بْنُ عَلِيٍّ ، عَنْ زَائِدَةَ ، قَالَ حَدَّثَنِي عَمْرُو بْنُ يَحْيَى الأَنْصَارِيُّ ، حَدَّثَنِي مُحَمَّدُ بْنُ يَحْيَى بْنِ حَبَّانَ ، عَنْ عَمْرِو بْنِ سُلَيْمِ بْنِ خَلْدَةَ الأَنْصَارِيِّ ، عَنْ أَبِي قَتَادَةَ ، صَاحِبِ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ دَخَلْتُ الْمَسْجِدَ وَرَسُولُ اللَّهِ صلى الله عليه وسلم جَالِسٌ بَيْنَ ظَهْرَانَىِ النَّاسِ - قَالَ - فَجَلَسْتُ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَا مَنَعَكَ أَنْ تَرْكَعَ رَكْعَتَيْنِ قَبْلَ أَنْ تَجْلِسَ " . قَالَ فَقُلْتُ يَا رَسُولَ اللَّهِ رَأَيْتُكَ جَالِسًا وَالنَّاسُ جُلُوسٌ . قَالَ " فَإِذَا دَخَلَ أَحَدُكُمُ الْمَسْجِدَ فَلاَ يَجْلِسْ حَتَّى يَرْكَعَ رَكْعَتَيْنِ " .
I entered the mosque, when the Messenger of Allah (ﷺ) had been sitting among people, and I also sat down among them. Upon this the Messenger of Allah (ﷺ) said: What prevented you from offering two rak'ahs (of Nafl prayer) before sitting down? I said: Messenger of Allah, I saw you sitting and people sitting (around you and I, therefore, sat in your company). He (the Holy Prophet) then said: When anyone among you enters the mosque, he should not sit till he has observed two rak'ahs.