Sending blessings upon the messenger of Allah salla Allahu alayhi wasalam.

 Sending blessings upon the messenger of Allah salla Allahu alayhi wasalam. 

Allah says, 

Al-Ahzab 33:56

Indeed, Allāh confers blessing upon the Prophet, and His angels [ask Him to do so]. O you who have believed, ask [Allāh to confer] blessing upon him and ask [Allāh to grant him] peace.

One of the companion asked the messenger of Allah salla Allahu alayhi wasalam how to send him the salam, 

Then the prophet PBUH said, 

Narrated `Abdur-Rahman bin Abi Laila:

Ka`b bin 'Ujra met me and said, "Shall I give you a present? Once the Prophet (ﷺ) came to us and we said, 'O Allah's Messenger (ﷺ) ! We know how to greet you; but how to send 'Salat' upon you? He said, 'Say: Allahumma Salli ala Muhammadin wa 'ala `Ali Muhammadin, kama sal-laita 'ala all Ibrahima innaka Hamidun Majid. Allahumma barik 'alaMuhammadin wa 'ala all Muhammadin, kama barakta 'ala all Ibrahima, innaka Hamidun Majid."

Sahih al-Bukhari 6357.

This is the salawat the messenger of Allah salla Allahu alayhi wasalam taught his companions to make. 

In another hadith, 

It was narrated from Abu Humaid As-Sa’di that they said:

“O Messenger of Allah! We have been commanded to send peace and blessings upon you. How should we send peace and blessings upon you?” He said: “Say: Allahumma salli ‘ala Muhammadin wa azwajihi wa dhurriyatihi, kama sallayta ‘ala Ibrahim; wa barik ‘ala Muhammadin wa azwajihi wa dhurriyatihikama barakta ‘ala ali Ibrahim fil-‘alamin, innaka Hamidum Majid (O Allah, send Your grace, honour and mercy upon Muhammad and his wives and offspring, as You sent Your grace, honour and mercy upon Ibrahim. O Allah, send Your blessings upon Muhammad and his wives and offspring, as You sent Your blessings upon the family of Ibrahim among the nations, You are indeed Praiseworthy, Most Glorious).”

Sunan ibn Majah. 

Vol. 1, Book 5, Hadith 905.