Verse 56 of Surah Al-Ahzab, the basis for sending blessings (salawat) upon the Prophet.
Allah states that He and His angels send blessings upon the Prophet, and calls on the believers to do the same. This verse is why Muslims say 'peace and blessings be upon him' whenever the Prophet is mentioned, and it is the foundation of the durood recited in prayer.
- 33:56
إِنَّ ٱللَّهَ وَمَلَٰٓئِكَتَهُۥ يُصَلُّونَ عَلَى ٱلنَّبِىِّ ۚ يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ صَلُّوا۟ عَلَيْهِ وَسَلِّمُوا۟ تَسْلِيمًا
Innal laaha wa malaaa'i katahoo yusalloona 'alan Nabiyy; yaaa aiyuhal lazeena aamanoo salloo 'alaihi wa sallimoo tasleemaa
Sesungguhnya Allah dan malaikatNya berselawat (memberi segala penghormatan dan kebaikan) kepada Nabi (Muhammad s.a.w); wahai orang-orang yang beriman berselawatlah kamu kepadanya serta ucapkanlah salam sejahtera dengan penghormatan yang sepenuhnya.