Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1280 (DarusSalam) ⓘ

It was narrated that Abdullah said: "The Messenger of Allah said: 'Allah, the Mighty and Sublime, is As-Salam the source of peace; the One free from all faults), so when any one of you sits (during the prayer), let him say: At-tahiyyatu lillahi wasalawatu wat-tayibaat, as-salamu 'alaika ayah-Nabiyyu wa rahmatAllahi wa baraktuhu. As-salamu 'alaina a 'ala ibad illahis-salihin, ashadu an la ilaha ill Allah, wa ashhadu anna Muhammadan 'abduhu wa rasuluhu. (All compliments, prayers and pure words are due to Allah. Peace be upon you O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous slaves of Allah. I bear witness that that none has the right to be worshipped except Allah, and I bear witness that Muhammad is His slave and messenger.)" Then after that, let him choose whatever words he wants."

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا الْفُضَيْلُ، - وَهُوَ ابْنُ عِيَاضٍ - عَنِ الأَعْمَشِ، عَنْ شَقِيقٍ، عَنْ عَبْدِ اللَّهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِنَّ اللَّهَ عَزَّ وَجَلَّ هُوَ السَّلاَمُ فَإِذَا قَعَدَ أَحَدُكُمْ فَلْيَقُلِ التَّحِيَّاتُ لِلَّهِ وَالصَّلَوَاتُ وَالطَّيِّبَاتُ السَّلاَمُ عَلَيْكَ أَيُّهَا النَّبِيُّ وَرَحْمَةُ اللَّهِ وَبَرَكَاتُهُ السَّلاَمُ عَلَيْنَا وَعَلَى عِبَادِ اللَّهِ الصَّالِحِينَ أَشْهَدُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ ثُمَّ لْيَتَخَيَّرْ بَعْدَ ذَلِكَ مِنَ الْكَلاَمِ مَا شَاءَ ‏" ‏ ‏.‏