Can the funeral prayer be offered for one who did not pray?
Question

                Are we obliged to attend the funeral prayer of a person who calls themself a Muslim (or who believes in Allah), yet drinks alcohol and has never prayed or fasted a single day in their life?.
Praise be to Allah.
    Firstly: 

    Attending the funeral of a Muslim, i.e., washing him or 
    shrouding him or offering the prayer for him or burying him, is a communal 
    obligation; if there is someone among the Muslims who can do that, then it 
    becomes mustahabb for you and not obligatory. 

    It says in Zaad al-Mustaqni’: Washing the deceased, 
    shrouding him, offering the prayer for him and burying him is a communal 
    obligation (fard kifaayah).  

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in
    al-Sharh: It should be noted that with regard to every communal 
    obligation, if it is undertaken by one who can do it properly, it is waived 
    in the case of the others, but if there is only one person who can do it, 
    then in his case it becomes an individual obligation (fard ‘ayn).  

    The author says “burying him is a communal obligation”, and 
    that on which burial depends is also a communal obligation, and that on 
    which the prayer depends is also a communal obligation, thus carrying him 
    from his house to the prayer place is a communal obligation, and carrying 
    him from the prayer place to the graveyard is a communal obligation, because 
    that without which the obligatory duty cannot be done is also obligatory. 
    End quote from al-Sharh al-Mumti’, 5/265. 

    Secondly: 

    With regard to the one who does not pray, if he does not pray 
    at all he is a kaafir, whether he does not pray because of laziness or 
    because he denies that it is obligatory, according to the more correct of 
    the two scholarly opinions, because of a great deal of evidence, some of 
    which has been mentioned in the answer to question number
    5208 and
    83165. 

    Based on that, it is not permissible for you to offer the 
    funeral prayer for one who you know died not praying, because of the general 
    meaning of the verses in which Allaah says (interpretation of the meaning):“And 
    never (O Muhammad صلى الله عليه وسلم) 
    pray (funeral prayer) for any of them (hypocrites) who dies, nor stand at 
    his grave. Certainly they disbelieved in Allaah and His Messenger, and died 
    while they were Faasiqoon (rebellious, — disobedient to Allaah and His 
    Messenger صلى الله عليه وسلم)”

    [al-Tawbah 9:84]

    “It is not (proper) for the Prophet and those who believe 
    to ask Allaah’s forgiveness for the Mushrikoon, even though they be of kin, 
    after it has become clear to them that they are the dwellers of the Fire 
    (because they died in a state of disbelief)”

    [al-Tawbah 9:113]. 

    So the one who did not pray should not be washed or shrouded 
    or the prayer offered for him, and he should not be buried in the Muslim 
    graveyard, because he is a kaafir, as stated above. 

    As for the disobedient Muslim, such as the one who used to 
    drink alcohol but he prayed regularly and did not stop praying, the funeral 
    prayer should be offered for him, but the imam or scholar may refrain from 
    offering the funeral prayer for him, as a rebuke to deter people from doing 
    what he did and to scare those who are like him, but other people should 
    offer the funeral prayer for him. 

    And Allaah knows best.