Hadith
أَخْبَرَنَا أَبُو الأَشْعَثِ، أَحْمَدُ بْنُ الْمِقْدَامِ الْعِجْلِيُّ الْبَصْرِيُّ قَالَ حَدَّثَنَا الْمُعْتَمِرُ، قَالَ سَمِعْتُ أَبِي يُحَدِّثُ، عَنْ قَتَادَةَ، عَنْ أَبِي غَلاَّبٍ، - وَهُوَ يُونُسُ بْنُ جُبَيْرٍ - عَنْ حِطَّانَ بْنِ عَبْدِ اللَّهِ، أَنَّهُمْ صَلَّوْا مَعَ أَبِي مُوسَى فَقَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " إِذَا كَانَ عِنْدَ الْقَعْدَةِ فَلْيَكُنْ مِنْ أَوَّلِ قَوْلِ أَحَدِكُمُ التَّحِيَّاتُ لِلَّهِ الطَّيِّبَاتُ الصَّلَوَاتُ لِلَّهِ السَّلاَمُ عَلَيْكَ أَيُّهَا النَّبِيُّ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ السَّلاَمُ عَلَيْنَا وَعَلَى عِبَادِ اللَّهِ الصَّالِحِينَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ " .
It was narrated from Hittan bin Abdullah that:They prayed with Abu Musa and he said: "The Messenger of Allah (ﷺ) said: 'When you are sitting then let the first words that any of you says be: At-tahiyyatu lillahi was-salawatu wat-tayyibat, as-salamu 'alaika ayyuhan-Nabiyyu wa rahmatAllahi wa baraktuhu. As-salamu 'alaina wa 'ala 'ibad illahis-salihin, ashahdu an la illaha ill-Allah wa ashhadu anna Muhammadan 'abduhu wa rasuluhu (Allah compliments, prayers and pure words are due to Allah. Peace be upon you, O Prophet, and the mercy of Allah (SWT) and his blessings. Peace be upon us and upon the righteous slaves of Allah (SWT). I bear witness that none has the right to be worshipped except Allah and I bear witness that Muhammad is His slave and Messenger
Sahih · Abu Ghuddah
Sunan an-Nasa'i 1173 ·Book 12, Hadith 145·Also available on sunnah.com·