Warrad, the freed slave of Sayyiduna al-Mughirah bin Shu'bah (may Allah be pleased with him), relates that he (may Allah be pleased with him) wrote a letter to Sayyiduna Mu'awiyah bin Abi Sufyan (may Allah be pleased with them both) that when the Messenger of Allah (peace and blessings be upon him) gave the salam ending the prayer, he would say these words: 'La ilaha illallahu wahdahu la sharika lah, lahul-mulku wa lahul-hamdu wa huwa ala kulli shay'in qadir, Allahumma la mani'a lima a'tayta wa la mu'tiya lima mana'ta wa la yanfa'u dhal-jaddi minkal-jadd' (None is worthy of worship but Allah; He has no partner; the dominion and the praise are His, and He has power over all things. O Allah, none can withhold what You give, and none can give what You withhold, and the wealth of a wealthy person cannot avail him anything before You (before You only deeds matter)).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3016