Why is Ibraaheem (peace be upon him) singled out for mention in the Tashahhud?
Question

                Why do we send blessings and peace upon Ibraaheem (peace be upon him) in the prayer, and not upon the other Prophets? He is one of the five Messengers of strong will, but he is not the first or last of them, so why him, and if it is because he is the first one mentioned, why do we not send greetings upon ‘Eesa, Nooh and Moosa as well?
Praise be to Allah.
    Allah, may He be 
    glorified and exalted, singled out Sayyiduna Ibraaheem (blessings and peace 
    of Allah be upon him) for great favours and honour. He was described in the 
    Qur’an as an imam (leader), an ummah (a nation in himself), a haneef 
    (monotheist),  and devoted to Allah, may He be glorified and exalted; all 
    the Prophets who came after him were descended from him and the followers of 
    all religions (Muslims, Christians and Jews) believe in him. 

    Ibraaheem (peace 
    be upon him) is the best of the Prophets and Messengers after our Prophet 
    Muhammad (blessings and peace of Allah be upon him). Hence Allah has told us 
    that He took him as a close friend. “And 
    Allah did take Ibrahim (Abraham) as a Khaleel (an intimate friend)” 
    [an-Nisa’ 4:125]. 

    All the Prophets 
    who came after him are descended from him via Ishaaq and Ya‘qoob, apart from 
    Muhammad (blessings and peace of Allah be upon him), who is descended from 
    Ismaa‘eel ibn Ibraaheem. 

    Our Prophet 
    (blessings and peace of Allah be upon him) is closer to Ibraaheem than 
    anyone else. So Ibraaheem (peace be upon him) is the father of the Arabs and 
    the forefather of the Prophet (blessings and peace of Allah be upon him) in 
    terms of descent. 

    Ibraaheem is the 
    one whom the Prophet (blessings and peace of Allah be upon him) instructed 
    his community to follow. “Then, We have inspired you (O Muhammad SAW 
    saying): "Follow the religion of Ibraheem (Abraham) Haneefa (Islamic 
    Monotheism - to worship none but Allah)” [an-Nahl 16:123].

    Hence our Prophet 
    (blessings and peace of Allah be upon him) is the closest of people to 
    Ibraaheem (peace be upon him), and so are we, as his followers. 

    Allah, may He be 
    glorified and exalted, says (interpretation of the meaning):

    “Verily, 
    among mankind who have the best claim to Ibraheem (Abraham) are those who 
    followed him, and this Prophet (Muhammad SAW) and those who have believed 
    (Muslims)”

    [Aal ‘Imraan 
    3:68].

    And He says, 
    refuting the Jews and the Christians:

    “Ibraheem 
    (Abraham) was neither a Jew nor a Christian, but he was a true Muslim 
    Haneefa (Islamic Monotheism - to worship none but Allah Alone) and he was 
    not of Al-Mushrikoon”

    [Aal ‘Imraan 
    3:67]. 

    Shaykh Ibn 
    ‘Uthaymeen (may Allah have mercy on him) was asked: Why is Ibraaheem (peace 
    be upon him) singled out for the call of Tawheed, when all the Prophets 
    called people to Tawheed (belief in the Oneness of Allah)? 

    He replied: 

    All the Prophets 
    brought the message of Tawheed. Allah, may He be exalted, says 
    (interpretation of the meaning):

    “And 
    We did not send any Messenger before you (O Muhammad SAW) but We inspired 
    him (saying): La ilaha illa Ana (none has the right to be worshipped but I 
    (Allah)), so worship Me (Alone and none else)”

    [al-Anbiya’ 
    21:25].
    

    But Ibraaheem was 
    the father of the Arabs, and the father of the Israelites, and he called 
    people to pure Tawheed. The Jews and the Christians claimed to be his 
    followers, but the Muslims are the ones who are his followers. He (peace and 
    blessings be upon him) was chosen to be the father of the Prophets; he is 
    the promoter of pure monotheism and we are instructed to follow him, because 
    we are closer to Ibraaheem, as Allah, may He be exalted, says 
    (interpretation of the meaning):

    “Verily, 
    among mankind who have the best claim to Ibraheem (Abraham) are those who 
    followed him, and this Prophet (Muhammad SAW) and those who have believed 
    (Muslims)”

    [Aal ‘Imraan 
    3:68].

    And He says, 
    refuting the Jews and the Christians:

    “Ibraheem 
    (Abraham) was neither a Jew nor a Christian, but he was a true Muslim 
    Haneefa (Islamic Monotheism - to worship none but Allah Alone) and he was 
    not of Al-Mushrikoon”

    [Aal ‘Imraan 
    3:67]. 

    Liqa’ al-Baab 
    al-Maftooh, 
    189/question no. 7 

    Al-‘Allaamah Badr 
    ad-Deen al-‘Ayni al-Hanafi (may Allah have mercy on him) noted another point 
    with regard to this issue, as he said: 

    If it is said: Why 
    was Ibraaheem (peace be upon him) singled out from among all the other 
    Prophets (peace be upon them) to be mentioned during the prayer? 

    I say: That is 
    because on the night of the Mi‘raaj, the Prophet (blessings and peace of 
    Allah be upon him) saw all the Prophets and Messengers, and he greeted each 
    Prophet with salaam, but none of them sent greetings to his ummah apart from 
    Ibraaheem (peace be upon him). Hence the Prophet (blessings and peace of 
    Allah be upon him) instructed us to send blessings upon him at the end of 
    every prayer until the Day of Resurrection, in response to his kindness. 

    It was also said 
    that when Ibraaheem (peace be upon him) had finished building the Ka‘bah, he 
    prayed for the ummah of Muhammad (blessings and peace of Allah be upon him), 
    saying: O Allah, whoever performs pilgrimage to this House from the ummah of 
    Muhammad, give him greetings from me; and his family and children also 
    offered this supplication, so we are instructed to remember them in the 
    prayer, in response to their kind deed. End quote. 

    Sharh Sunan Abi 
    Dawood 
    by al-‘Ayni, 4/260 

    And Allah knows 
    best.