It was narrated that Ibn Mas'ud said:

"Before the tashahhud was enjoined, when we prayed we used to say: 'Peace (As-Salam) be upon Allah (Subhanahu-wa-Taala), pace be upon Jibril, peace be upon Mika'il.' The Messenger of Allah ﷺ said: 'Do not say this, for indeed Allah (Subhanahu-wa-Taala), the Mighty and Sublime, is As-Salam. Rather 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.)"

أَخْبَرَنَا سَعِيدُ بْنُ عَبْدِ الرَّحْمَنِ أَبُو عُبَيْدِ اللَّهِ الْمَخْزُومِيُّ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنِ الأَعْمَشِ، وَمَنْصُورٌ، عَنْ شَقِيقِ بْنِ سَلَمَةَ، عَنِ ابْنِ مَسْعُودٍ، قَالَ كُنَّا نَقُولُ فِي الصَّلاَةِ قَبْلَ أَنْ يُفْرَضَ التَّشَهُّدُ السَّلاَمُ عَلَى اللَّهِ السَّلاَمُ عَلَى جِبْرِيلَ وَمِيكَائِيلَ . فَقَالَ رَسُولُ اللَّهِ ﷺ " لاَ تَقُولُوا هَكَذَا فَإِنَّ اللَّهَ عَزَّ وَجَلَّ هُوَ السَّلاَمُ وَلَكِنْ قُولُوا 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 " .