IsLaMiC

In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committe, issues the following fatwa:
Allah Almighty says: "Lo! Allah and His angels shower blessings on the Prophet. O ye who believe! Ask blessings on him and salute him with a worthy salutation" (Al-Ahzaab: 56).
Scholars are of the opinion that Allahs Blessing of His Prophet is a mercy that He Almighty bestows on him. Likewise, the angels prayers for the Prophet, peace and blessings be upon him, are a means of seeking forgiveness for him, and the believers seeking blessings for the Prophet, peace and blessings be upon him, is a supplication for him. We are enjoined to pray to Allah to bestow more honor and mercy on His Prophet, peace and blessings be upon him.
Various texts prove that Allah has bestowed on His Prophet, peace and blessings be upon him, countless blessings, yet we are still enjoined to seek Allahs Blessing for the Prophet. This is an expression of our love for the Prophet, peace and blessings be upon him, which is in turn an indication of our deep faith in Allah.
It is reported that the Prophet, peace and blessings be upon him, says: None of you is considered a true believer until he loves me more than his parents and all other people. And there are other versions conveying the same meaning.
Some scholars say that by seeking Allahs Blessing for the Prophet, peace and blessings be upon him, we are not interceding for him since we are not in a position to intercede for such a great person as the Prophet. However, Allah has enjoined us to reward those who do us good and pray for them if we cannot fully reward them. Since we cannot reward our Prophet for what he has done for us then we are enjoined to pray for him.
Shedding more light on the question in point, we can say that some scholars maintain that one should send peace and blessings upon the Prophet, peace and blessings be upon him, once in a lifetime, some say it must be done whenever one hears the name of the Prophet mentioned, some say that it must be said whenever one makes a supplication (Du`aa') and others say it must be said during the prayers after the Tashahhud.
A group of scholars are of the opinion that it is recommended but not obligatory. However, the evidence concerning such an issue could be verified by referring to the authentic books of Hadith.
There is no specific formula for sending peace and blessings upon the Prophet Muhammad, peace and blessings be upon him. However, some scholars say that the best formula is the one mentioned in the following narration of Al-Bukhari:
"O Allah! Send Your Mercy on Muhammad and on the family of Muhammad, as You sent Your Mercy on Abraham and on the family of Abraham, for You are the Most Praise-worthy, the Most Glorious. O Allah! Send Your Blessings on Muhammad and the family of Muhammad, as You sent your Blessings on Abraham and on the family of Abraham, for You are the Most Praise-worthy, the Most Glorious."
In this context, it is noteworthy that the above-mentioned formula is known As-Salaah Al-Ibraheemiyyah which is uttered frequently in the last part of the Tasahhud in daily prayers. The authentic books of Hadith indicate that it was the one that the Prophet taught his Companions when the verse enjoining Muslims to pray for the Prophet, peace and blessings be upon him, was revealed.
Here are some Hadiths that encourage a Muslim to send peace and blessings upon the Prophet Muhammad, peace and blessings be upon him:
1-The Prophet, peace and blessings be upon him, says, "He who sends(Allah's) blessings upon me once, Allah will bless him ten times." (Reported by Muslim)
2-The Prophet, peace and blessings be upon him, says, " Whenever someone seeks Allahs blessings for me, Allah returns the soul to my body until I reply to his salutation." (Reported by Abu-Dawood)
3-Also, He says: "Those who are most deserving of my intercession on the Day of Judgement are those who used to increasingly seek Allahs Blessing for me. (Reported by At-Tirmidhi)
4-Another hadith states: "The miser is the one who hears my name mentioned and does not seek blessings for me. (Reported by At-Tirmidhi)
In his book "Al-Adhkaar", Imam An-Nawawi says that one should seek both peace and blessings for the Prophet, but not just one of them, and that it is preferable to start any supplication by praising and glorifying Allah, then seeking blessings and peace for the Prophet. It should be followed by asking Allah what one wants, and then one ends the supplication by seeking blessings and peace for the Prophet, peace and blessings be upon him.
Allah Almighty knows best.