As for the Prophet's saying: "Ash-Hadu Alla Ilaha Illa Allah wa Ashhadu Anna Muhammadan `Abduhu warasuluh," it includes a testimony for Allah with oneness and for His Messenger with servitude to his Lord and that he was given the message of Allah, so he is a servant not to be worshipped and a messenger whom should be followed and obeyed. It is permissible for a Muslim to send peace and blessings upon the Messenger of Allah (peace be upon him) using the Abrahamic Salah that was reported from the Prophet (peace be upon him). Many Hadiths were reported about this Salah, of which the Hadith that was reported in Sahih Al Bukhari and Sahih Muslim on the authority of `Abdur-Rahman ibn Abu Layla who said: "Ka`b ibn `Ujrah met me and said: "Shall I not give you a present I got from the Prophet (peace be upon him)?" `Abdur-Rahman said: "Yes, give it to me." I said: "We asked Allah's Messenger (peace be upon him) saying: 'O Allah's Messenger! How should one (ask Allah to) send blessings on you, the the Prophet's family, for Allah has taught us how to salute you (during Salah)?' He said: 'Say: "Allahumma Salli `Ala Muhammadin Wa`la 'Ali Muhammad Kama Sallayta `Ala Ibrahim Wa`la 'Ali Ibrahim Innaka Hamidun Majid Allahumma Barik `Ala Muhammadin Wa`la 'Ali Muhammadin Kama Barakta `Ala Ibrahim Wa`la 'Ali Ibrahim Innaka Hamidun Majid." [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].'" [Sahih Al Bukhari, No. 3370 and Sahih Muslim No. 406].
It was reported in Sahih Al Bukhari and Sahih Muslim on the authority of Abu Humayd As-Sa`idy (may Allah be pleased with him) said: "The people asked Allah's Messenger! How shall we (ask Allah to) send blessings on you?" Allah's Messenger (peace be upon him) replied: "Say: Allahumma Salli `Ala Muhammadin Wa`la 'Ali Muhammadin Kama Sallayta `Ala Ibrahim Wa`la 'Ali Ibrahim Innaka Hamidun Majid Allahumma Barik `Ala Muhammadin Wa`la 'Ali Muhammadin Kama Barakta `Ala Ibrahim Wa`la 'Ali Ibrahim Innaka Hamidun Majid [O Allah! Send Your Mercy on Muhammad and on his wives and on his offspring, as You sent Your Mercy on Abraham's family; and send Your Blessings on Muhammad and on his offspring, as You sent Your Blessings on Abraham's family, for You are the Most Praise-worthy, the Most Glorious]." [Sahih Al Bukhari, No. 3369 and Sahih Muslim, No. 407].
And the saying of Ka`b (may Allah be pleased with him) "Shall I not give you a present I got from the Prophet (peace be upon him)," it shows the care of the Pious Predecessors for the Prophet's Sunnah and their happiness with it, moreover they used to count it one of the precious things, as they used to be glad at hearing it and exchange it in between.
Sending peace and blessing to the Messenger of Allah means mentioning the Prophet in the highest assembly of angels, the Salah of angels and the believers on him means asking Allah to mention him in the highest assembly, and the meaning is to ask for more mentioning.
The meaning of the Prophet's saying: "Allahumma Barik `Ala Muhammadin wa`la `Ali Muhammad," the meaning of Barik is bless and increase which is an invocation to increase and double goodness.
A Muslim may choose whatever supplications he wants to ask his Lord. It was authentically reported from the Prophet (peace be upon him) in this position many kinds of supplications which we shall speak about in the following articles.