سنن النسائي

It was narrated that Abdullah said: "The Messenger of Allah (ﷺ) 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."