What is the ruling on the imam saying in his Qunoot du‘aa’: O Allah, send one of Your dogs against him”?
Question

                What is the ruling on this supplication: “O Allah, send one of Your dogs against them” and saying it in Qunoot? What is the ruling on the prayer of one who prays behind one who says a du‘aa’ like this?.
Praise be to Allah.
      There is nothing wrong with offering supplication like 
      this, praying against the enemies of Allah and the enemies of His 
      religion. It is narrated in the Sunnah that the Prophet (blessings and 
      peace of Allah be upon him) offered this supplication against one of his 
      enemies, namely the cousin of the Prophet (blessings and peace of Allah be 
      upon him), the son of his uncle Abu Lahab. 

    It was narrated by al-Haakim (3984) and by al-Bayhaqi in 
    al-Dalaa’il (622) that Lahab ibn Abi Lahab used to revile the Prophet 
    (blessings and peace of Allah be upon him), and the Prophet (blessings and 
    peace of Allah be upon him) said: “O Allah, send Your dog against him.” He 
    went out with a caravan, heading towards Syria. He halted at some place and 
    said: I am afraid of the prayer of Muhammad (blessings and peace of Allah be 
    upon him). They said to him: No (don’t worry). They surrounded him with 
    their luggage and stood guard over him, then a lion came and snatched him 
    and took him away. 

    Al-Haakim said: Its isnaad is saheeh. And al-Dhahabi agreed 
    with him. 

    It was also narrated by Abu Na‘eem in al-Dalaa’il 
    (220), where he mentioned his name as being ‘Utbah ibn Abi Lahab, and in 
    that report it says: “O Allah, send against him one of Your dogs.” 

    The hadeeth was classed as hasan by al-Haafiz Ibn Hajar in 
    Fath al-Baari (4/39), al-‘Ayni in ‘Umdat al-Qaari’ (16/51), 
    al-Shawkaani in Nayl al-Awtaar (5/80), and al-San‘aani in Subul 
    al-Salaam (2195).  

    It should be noted that it may be appropriate to pray for 
    destruction for a kaafir, or it may be more appropriate to pray that he be 
    guided. That is according to the level of his hostility against the 
    Muslims. 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was 
    asked: 

    Can one pray for death, destruction and punishment against 
    the apostate or kaafir, or should we pray that he be guided? When should we 
    pray for him and when should we pray against him? 

    He replied: 

    If this apostate is harming the slaves of Allah and 
    transgressing against their rights, then there is nothing wrong with praying 
    against him and asking that he be destroyed, so as to ward off his evil. If 
    that is not the case, then it is better to pray for him to be guided instead 
    of praying against him to be destroyed. However, the duty of those who are 
    in authority towards the apostates is to call them to Islam and to give them 
    time, no more than three days. They have the choice of giving them this 
    time, if they think that there is an interest to be served by delaying their 
    execution. Then when the time is up, if the apostate insists on his 
    apostasy, then he must be executed, because the Prophet (blessings and peace 
    of Allah be upon him) said: “Whoever changes his religion, execute him.” End 
    quote. 

    Fataawa Islamiyyah, 4/232. 

    And Allah knows best.