Ruling on a du‘aa’ called “Du‘aa’ Kumayl ibn Ziyaad”
Question

                Is dua kumail, which the shia read every week permissible for us to read? Also, if a dua is unauthentic, is it wrong to read it even though its very good?
Also, in the last rakaah of salaat when reading durood sharif, is it ok to read allahumma saliala muhammad, wa ala aali muhamad, kamasalayta aala ibrahim wa aala aali ibrahim inaka hameedum majeed.' is just reciting the tashahhud followed by this enough (without any dua at the end)?
Praise be to Allah.
    Firstly: 

    “Du‘aa’ Kumayl” is a very 
    well-known supplication among the Shi‘ah, who are very keen to recite it 
    every week on the night of Friday, and on the night of the fifteenth of the 
    month of Sha‘baan (Laylat an-Nusf min Sha‘baan), in accordance with reports 
    that speak of its virtue and far-reaching effect in self-discipline, and 
    because of what it contains of sublime meanings – or so they claim. 

    Muhammad Baaqir al-Majlisi said 
    concerning this du‘aa’: “It is the best of du‘aa’s and is the du‘aa’ of al-Khadr 
    (peace be upon him). It was taught by Ameer al-Mu’mineen (peace be upon him) 
    to Kumayl, who was one of his closest companions.” 

    Al-Qummi said: “It is one of the 
    well-known supplications, and is to be recited on the night of the fifteenth 
    of Sha‘baan and the night of Friday; it suffices against the evil of one’s 
    enemies and it opens the door to provision and forgiveness of sins.” 

    See the following link: 
    


    http://www.islam4u.com/almojib.php?rid-636 

    In the report of this du‘aa’ it 
    says that ‘Ali ibn Abi Taalib said to Kumayl ibn Ziyaad: “Sit down, O Kumayl. 
    If you memorise this du‘aa’ and recite it every week on the night of Friday, 
    or once in a month, or once in a year, or once in your life, you will be 
    sufficed and supported and granted provision, and you will never be without 
    forgiveness. 

    “O Kumayl, because you have 
    accompanied us for so long, we should give you what you ask for.” 

    Then he said: “O Allah, I ask 
    You by virtue of Your mercy which encompasses all things, and by virtue of 
    Your power by which You dominate all things and everything submits to it, 
    and by virtue of Your might by which You overcome all things, and by virtue 
    of Your power, which nothing can resist, and by virtue of Your greatness, 
    which encompasses all things, and by virtue of Your sovereignty, which 
    transcends all things, and by virtue of Your eternal Countenance which will 
    remain after all things cease to be, and by virtue of Your names which 
    filled the space of all things, and by virtue of Your knowledge which 
    encompasses all things, and by virtue of the light of Your Countenance which 
    illuminates all things; O Light, O Most Holy, O First of the first, O Last 
    of the last, O Allah, forgive me my sins which weaken all bonds. O Allah, 
    forgive me my sins which bring down divine wrath. O Allah, forgive me my 
    sins that remove blessings. O Allah, forgive me my sins which detain 
    supplication (and prevent it from reaching You). O Allah, forgive me my sins 
    which bring down calamity. O Allah, forgive me all the sins I have committed 
    and every error I have made… “

    This is a du‘aa’ with an 
    over-wrought poetic rhythm to it which does not sound like the words of any 
    Sahaabi, and it is far removed from the light of Prophethood. 

    This du‘aa’ does not have any 
    known chain of transmission from ‘Ali (may Allah be pleased with him) 
    according to Ahl as-Sunnah. Rather it is well-known among those who believe 
    that telling lies against Allah, His Messenger and His close friends is an 
    act of religious devotion and a means of drawing closer to Allah. 

    Secondly: 

    Even if we assume that all of 
    its words and meanings are good, it is not appropriate to call upon Allah 
    with this du‘aa’ and recite it regularly, because in addition to it being a 
    fabricated du‘aa’ that cannot be soundly attributed to Ameer al-Mu’mineen 
    ‘Ali (may Allah be pleased with him), it has also become a slogan or symbol 
    of the Raafidis and others of their ilk who follow innovation. It is stated 
    above that they regard it as holy, venerate it and hold it in high esteem. 
    Something that is like that should not be taken as a religious practice. 

    Shaykh al-Islam Ibn Taymiyah 
    (may Allah have mercy on him) said: 

    If it is more likely that a 
    mustahabb action will result in evil consequences, it is no longer mustahabb. 
    Therefore a number of the fuqaha’ were of the view that some mustahabb 
    actions should be abandoned if they have become symbols of the Raafidis (the 
    Shi‘ah), because this does not mean that an obligatory duty is being 
    abandoned. Rather doing that means that one is resembling them, and in that 
    case it becomes difficult to distinguish between a Sunni and a Raafidi (Shi‘i). 
    The interests served by being distinct from them, for the purpose of 
    shunning them and differing from them, is greater than the interests served 
    by doing this mustahabb action.

    End quote from Minhaaj as-Sunnah 
    an-Nabawiyyah (4/154) 

    Shaykh Muhammad ibn Ibraaheem 
    (may Allah have mercy on him) said: 

    Some of the scholars 
    emphatically disallowed resembling the followers of innovation in that which 
    has become their symbols or slogans, even if it is Sunnah in principle. Both 
    groups are agreed that it is not allowed to resemble the followers of 
    innovation in that which is a symbol or slogan for them.

    End quote from Fataawa wa 
    Rasaa’il Muhammad ibn Ibraaheem (6/202) 

    See also the answer to question 
    no. 27237 and 6745 

    Thirdly: 

    The questioner asks whether it 
    is acceptable, after reciting as-salaah al-Ibraaheemiyyah (“durood sharif”) 
    in the final tashahhud, to recite this du‘aa’ only, followed immediately by 
    the salaam, with no other du‘aa’ in between. 

    If what he means by du‘aa’ here 
    is this du‘aa’ that is known as the du‘aa’ of Kumayl ibn Ziyaad, then we 
    have stated above that this is not acceptable and is in fact not allowed. 

    But if what he means is to ask 
    about the ruling on saying the salaam immediately after finishing as-salaah 
    al-Ibraaheemiyyah, without saying any du‘aa’, then it is well known that 
    saying du‘aa’ in the final tashahhud, after sending blessings upon the 
    Prophet (blessings and peace of Allah be upon him) and before saying the 
    salaam, is Sunnah but not obligatory. So it is permissible for the 
    worshipper to say the salaam straight away, without saying du‘aa’. 

    It says in al-Mawsoo‘ah al-Fiqhiyyah 
    (27/98): 

    It is Sunnah for the worshipper, 
    after reciting the final tashahhud, to offer any du‘aa’ he wants, because 
    the Prophet (blessings and peace of Allah be upon him) said: “When one of 
    you sits during the prayer, let him say ‘At-tahiyyaatu Lillah…’ until 
    the end, then let him ask Allah for whatever he wants or likes.” 

    According to a report narrated 
    by al-Bukhaari: “Then let him choose whatever du‘aa’ he likes, and say it.” 
    According to another report, narrated by Muslim, he said: “Then after that 
    let him ask for whatever he wants.”

    End quote. 

    It says in Asna al-Mataalib 
    (1/166): 

    “It is mustahabb to say du‘aa’ 
    after that” means after sending blessings upon him and his family in the 
    final tashahhud “as he wants” of matters of this world and of the Hereafter. 
    End quote. 

    Based on that, if the worshipper 
    only sends blessings upon the Prophet (blessings and peace of Allah be upon 
    him) then says the tasleem, and does not say du‘aa’ for anything, there is 
    nothing wrong with that, but he is neglecting a Sunnah. 

    Before saying the salaam, it is 
    confirmed that one should seek refuge with Allah from four things: from the 
    punishment of Hell, from the punishment of the grave, from the trials of 
    life and death, and from the fitnah of the false messiah, the Dajjaal, 
    because the Prophet (blessings and peace of Allah be upon him) enjoined 
    that, according to a report narrated by Muslim (588) from Abu Hurayrah, who 
    said: “When one of you has finished the final tashahhud, let him seek refuge 
    with Allah from four things: from the punishment of Hell, from the 
    punishment of the grave, from the trials of life and death, and from the 
    evil of the Dajjaal.” 

    An-Nawawi (may Allah have mercy 
    on him) said: This clearly indicates that this is mustahabb in the final 
    tashahhud. End quote. 

    There are other du‘aa’s which it 
    is also mustahabb for the worshipper to say after finishing the final 
    tashahhud. For more information, please see the answer to question no.
    5236.

    And Allah knows best.