How to Send Blessings Upon Prophet Muhammad
Question

I am one of those who send blessings upon the Prophet between 50 and 100 times a day, according to circumstances. I say: “Allahumma salli `ala Muhammadin wa ali Muhammad (O Allah, send blessings upon Muhammad and the family of Muhammad).”
There are some people who tell me that my sending blessings upon the Messenger of Allah is lacking. Can you tell us – may Allah reward you with good – what is the ideal way to send blessings upon the master of mankind, and is the way I am doing it really lacking?
Praise be to Allah.Virtues of sending blessings upon Prophet Muhammad
Sending blessings upon Prophet Muhammad (blessings and peace of Allah be upon him) is one of the greatest acts of worship encouraged in Islam, and it is one of the most beneficial supplications for a person in this world and the hereafter, and it is one of the requirements of loving, venerating and respecting the Prophet (blessings and peace of Allah be upon him) and giving him his rights.
How to Send Blessings to Prophet Muhammad
With regard to the ideal way of sending blessings upon the master of mankind (blessings and peace of Allah be upon him), there are a number of ways of doing that, which you can find in the book Sifat Salat An-Nabi (sallallahu `alayhi wa sallam) by Al-`Allamah Al-Albani (may Allah have mercy on him), p. 165 of the edition published by Maktabat Al-Ma `arif in Riyadh [this book is available in English as The Prophet`s Prayer Described].
Among the soundest and most well-known of these ways are the two ways that the Prophet (blessings and peace of Allah be upon him) taught his Companions (may Allah be pleased with them) when they asked him how they should send blessings upon him (blessings and peace of Allah be upon him). These two ways are as follows:

 “Allahumma salli `ala Muhammad wa `ala ali Muhammad kama salayta `ala Ibrahim wa `ala ali Ibrahim, innaka hamidun majid. Allahumma barik `ala Muhammad wa `ala ali Muhammad kama barakta `ala Ibrahim wa `ala ali Ibrahim, innaka hamidun majid (O Allah, send prayers upon Muhammad and upon the family of Muhammad, as You sent prayers upon Ibrahim and upon the family of Ibrahim; You are indeed Worthy of Praise, Full of Glory. O Allah, send blessings upon Muhammad and upon the family of Muhammad as You sent blessings upon Ibrahim and upon the family of Ibrahim; You are indeed Worthy of Praise, Full of Glory).” (Narrated by Al-Bukhari, 3700 and Muslim, 406 from the Hadith of Ka`b ibn `Ajrah (may Allah be pleased with him)).


“Allahumma salli `ala Muhammadin wa `ala azwajihi wa dhurriyyatihi kama salayta `ala Ibrahim, wa barik `ala Muhammadin wa `ala azwajihi wa dhurriyyatihi kama barakta `ala ali Ibrahim, innaka hamidun majid (O Allah, send Your salah (grace, honour and mercy) upon Muhammad and upon his wives and offspring, as You sent Your salah upon Ibrahim, and send Your blessings upon Muhammad and upon his wives and offspring, as You sent Your blessings upon the family of Ibrahim. You are indeed Praiseworthy, Most Glorious).”  (Narrated by Al-Bukhari, 3369 and Muslim, 407 from the Hadith of Abu Humayd As-Sa`idi (may Allah be pleased with him))

The Prophet (blessings and peace of Allah be upon him) did not choose anything but that which is noblest and best. (Rawdat At-Talibin by An-Nawawi, 11/66; Fat-h Al-Bari by Ibn Hajar, 11/166; Sifat Salat An-Nabi by Al-Albani, p. 175; Al-Mawsu`ah Al-Fiqhiyyah Al-Kuwaitiyyah, 27/97)
It is better to vary the phrases used, switching between the versions that have been narrated, sometimes reciting one and sometimes reciting another, so as to follow the Sunnah and Shari`ah, and so that always reciting one version does not lead to neglecting another which is also proven, and because there are many other benefits in doing so which will not be attained by always reciting only one and not the other.
But we should point out that it is not prescribed to combine and mix these phrases so as to produce a combination of all of them in one; rather that is contrary to the Sunnah, as was stated by a number of scholars. (Majmu` Al-Fatawa by Ibn Taymiyyah, 22/335, 458; 24/242, 247; Jala` Al-Ifham by Ibn Al-Qayyim, p. 373; Qawa`id Ibn Rajab, p. 14 and Ash-Sharh Al-Mumti` by Ibn `Uthaymin, 2/56, 65; 3/29, 98)
All of this has to do with sending blessings upon him (blessings and peace of Allah be upon him) after the Tashahhud in the prayer.
Can I send blessings to Porphet Muhammad by saying ‘Allahumma salli `ala Muhammadin wa ali Muhammad’?
With regard to sending blessings upon him (blessings and peace of Allah be upon him) by saying “Allahumma salli `ala Muhammadin wa ali Muhammad (O Allah, send blessings upon Muhammad and the family of Muhammad) outside of the prayer, if what your friend means is that it is lacking in comparison to the complete wording that has been narrated, then this is correct. But if what he meant was that it is not valid or that it does not count as sending blessings upon the Messenger (blessings and peace of Allah be upon him), then that is not the case; rather it is sending blessings upon the Prophet (blessings and peace of Allah be upon him) and its wording is correct and fulfils the purpose. The scholars still say, “Allahumma salli `ala Muhammad” or “sallallahu `alayhi wa sallam (may Allah send blessings and peace upon him)” and the like. The matter is broad in scope, in sha Allah.
Al-Hafidh ibn Hajar stated in Fat-h Al-Bari (11/166) that the majority of scholars think that any wording that fulfils the purpose of sending blessings upon him is acceptable, but in the prayer one should keep to the wording that has been narrated and not omit any part of it, so as to be sure of following the Sunnah and what is narrated from the Prophet (blessings and peace of Allah be upon him).
With regard to this wording also, it is restricted to sending blessings (Salah) and not Salam, whereas Allah, may He be Glorified, has instructed us to send both blessings and greeting of peace upon him, as He says (interpretation of the meaning):
{Allah sends His Salah (Graces, Honours, Blessings, Mercy, etc.) on the Prophet (Muhammad SAW) and also His angels too (ask Allah to bless and forgive him). O you who believe! Send your Salah on (ask Allah to bless) him (Muhammad (blessings and peace of Allah be upon him)), and (you should) greet (salute) him with the Islamic way of greeting (salutation i.e. As-Salamu `Alaykum).} [Al-Ahzab 33:56]
The scholars have stated that it is disliked for a person to always mention Salah (blessings) without Salam (greeting of peace), or to always mention Salam without Salah. But if he mentions both of them, or mentions Salah on its own sometimes, or Salam on its own sometimes, then he is following the verse. And Allah knows best.” (End quote from Fat-h Al-Bari, 11/167)
And Allah knows best.