[Machine] I entered the mosque and the Messenger of Allah ﷺ was sitting amongst the people. So, I sat down. Then the Messenger of Allah ﷺ said, "What prevented you from praying two units (rak'ahs) before sitting down?" I replied, "I saw you sitting, and the people were also sitting." He said, "When one of you enters the mosque, they should not sit down until they have prayed two units (rak'ahs)."  

دَخَلْتُ الْمَسْجِدَ وَرَسُولُ اللهِ ﷺ جَالِسٌ بَيْنَ ظَهْرَيِ النَّاسِ فَجَلَسْتُ فَقَالَ رَسُولُ اللهِ ﷺ مَا مَنَعَكَ أَنْتَرْكَعَ رَكْعَتَيْنِ قَبْلَ أَنْ تَجْلِسَ؟ قَالَ قُلْتُ إِنِّي رَأَيْتُكَ جَالِسًا وَالنَّاسُ جُلُوسٌ قَالَ وَإِذَا دَخَلَ أَحَدُكُمُ الْمَسْجِدَ فَلَا 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. (Using translation from Muslim 714b)   

عَنْ أَبِي قَتَادَةَ صَاحِبِ رَسُولِ اللهِ ﷺ قَالَ دَخَلْتُ الْمَسْجِدَ وَرَسُولُ اللهِ ﷺ جَالِسٌ بَيْنَ ظَهْرَانِي النَّاسِ قَالَ فَجَلَسْتُ فَقَالَ رَسُولُ اللهِ ﷺ مَا مَنَعَكَ أَنْ تَرْكَعَ رَكْعَتَيْنِ قَبْلَ أَنْ تَجْلِسَ؟ قَالَ فَقُلْتُ يَا رَسُولَ اللهِ رَأَيْتُكَ جَالِسًا وَالنَّاسُ جُلُوسٌ قَالَ إِذَا دَخَلَ أَحَدُكُمُ الْمَجْلِسَ فَلَا يَجْلِسْ حَتَّى يَرْكَعَ رَكْعَتَيْنِ