1. Variants of the Phrase in Arabic

After mentioning one of the names of God, such as Allah, an expression of worship is used as opposed to the phrases of supplication used for regular individuals. These include:

2. In the Qur'an

Giving these blessings is often taken from Surah al-Ahzab (33), Ayah 56:

إِنَّ ٱل‍لَّٰهَ وَمَلَائِكَتَهُ يُصَلُّونَ عَلَىٰ ٱلنَّبِيِّ يَا أَيُّهَا ٱلَّذِينَ آمَنُوا۟ صَلُّوا۟ عَلَيْهِ وَسَلِّمُوا۟ تَسْلِيمًا
"Surely God and His angels bless the Prophet; O you who believe! Send blessings on him and salute him with a (becoming) salutation."^{[Quran 33:56 (Translated by Shakir)]}

3. In Tafsir

"Blessings of God be upon him and his family and peace". https://handwiki.org/wiki/index.php?curid=1890579

The scholar ibn Kathir, titled the section in his Tafsir ibn Kathir regarding this verse, "The Command to say salawat upon the Prophet (Muhammad)". This point is further founded in the saying by Muhammad, "The miser is the one in whose presence I am mentioned, then he does not send the Salam upon me." This was recorded in Musnad Ahmad ibn Hanbal.

4. In Hadiths

Blessings of God be upon him and peace. https://handwiki.org/wiki/index.php?curid=1842186

The evidence for sending ṣalawāt on Muhammad is not limited to the Qurʻān. It is also found in hadiths about Muhammad.

Al-Tirmidhi recorded that Abu Hurairah said, "The Messenger of Allah said, 'May he be humiliated, the man in whose presence I am mentioned and he does not send Salaam upon me; may he be humiliated, the man who sees the month of Ramadan come and go, and he is not forgiven; may he be humiliated, the man whose parents live to old age and they do not cause him to be granted admittance to Paradise.'" Al-Tirmidhi said that this hadith was ḥasan gharib "Good but only reported once".

In Sahih Muslim, Sunan Abu Dawood, Jami` at-Tirmidhi, and al-Sunan al-Sughra, four of the Six major Hadith collections, recorded that Abu Hurairah said, "The Messenger of Allah said: 'Whoever sends one Salaam upon me, Allah will send ten upon him.'"

Ahmad ibn Hanbal reported in his Musnad Ahmad ibn Hanbal that the Companion of Muhammad, Abu Talha ibn Thabit, said:

One morning the Messenger of Allah was in a cheerful mood and looked happy. They said, "O Messenger of Allah, this morning you are in a cheerful mood and look happy." He said, "Of course, just now someone [an angel] came to me from my Lord [Allah] and said, 'Whoever among your Ummah sends Salaam upon you, Allah will record for him ten good deeds and will erase for him ten evil deeds, and will raise his status by ten degrees, and will return his greeting with something similar to it.'"

Al-Bayhaqi reports that Abu Hurairah said that Muhammad said, "Send the Salaam on Allah's messengers and prophets for Allah sent them as He sent me."

5. Ruling on Abbreviating the Phrase

Scholars of the Salafi branch of Islam practised in Saudi Arabia have instructed their followers not to abbreviate the salawat upon Muhammad. For example, Abd al-Aziz ibn Baz, the Grand Mufti of Saudi Arabia, said:

As it is prescribed to send prayers upon the Prophet (peace and prayers of Allah be upon him) in prayer when saying the tashahhud, and it is prescribed when giving khutbahs, saying Du’a and praying for forgiveness, and after the Adhan, and when entering and exiting the mosque, and when mentioning him in other circumstances, so it is more important to do so when writing his name in a book, letter, article and so on. So it is prescribed to write the prayers in full so as to fulfil the command that Allah has given to Muslims, and so that the reader will remember to say the prayers when he reads it. So one should not write the prayers on the Prophet (peace and prayers of Allah be upon him) in short form such as writing (S) or (SAWS) etc, or other forms that some writers use, because that is going against the command of Allah in His Book, where He says (interpretation of the meaning):

"Send your Salaah on (ask Allah to bless) him (Muhammad), and (you should) greet (salute) him with the Islamic way of greeting (salutation, i.e. As‑Salaamu ‘Alaykum)" [Qurʾān 33:56]

And that (writing it in abbreviated form) does not serve that purpose and is devoid of the virtue of writing "salla Allaahu ‘alayhi wa salaam (May Allah send prayers and peace upon him)" in full. Moreover the reader may not take notice of it and may not understand what is meant by it. It should also be noted that the symbol used for it is regarded as disapproved by the scholars, who warned against it.