What is the Qadiani (Ahmadiyyah) sect? Is it permissible for a Muslim to marry one of them?
Question

                I just wana know about Ahmedi Fiqqah. the reason is that one of my friend start loving an Ahmedi, though i told him that its wrong but he is so much involve now. i just want the answer so that i fwd him.
Praise be to Allah.
    In the answer to question no.
    4060 we have explained that this 
    group, which is known as Ahmadiyyah or Qadianiyyah, the followers of Mirza 
    Ghulam Ahmad, are kaafirs. In that answer you will find a discussion of 
    their kaafir beliefs and what the scholars have said about them.

    Based on this, it is not permissible for a Muslim to marry 
    one of them or to give his daughter in marriage to them, because they are 
    kaafirs and apostates, and Allaah says (interpretation of the meaning): 

    “And do not marry Al-Mushrikaat (idolatresses) till they 
    believe (worship Allaah Alone). And indeed a slave woman who believes is 
    better than a (free) Mushrikah (idolatress), even though she pleases you. 
    And give not (your daughters) in marriage to Al‑Mushrikoon till they believe 
    (in Allaah Alone) and verily, a believing slave is better than a (free) 
    Mushrik (idolater), even though he pleases you. Those (Al-Mushrikoon) invite 
    you to the Fire, but Allaah invites (you) to Paradise and forgiveness by His 
    Leave, and makes His Ayaat (proofs, evidences, verses, lessons, signs, 
    revelations, etc.) clear to mankind that they may remember”

    [al-Baqarah 2:221]

    al-Sa’di (may Allaah have mercy on him) said in his Tafseer 
    (p. 99): 

    i.e., do not marry mushrik women so long as they still 
    believe in shirk, until they believe, for a believing woman, no matter how 
    ugly she is, is better than a mushrik woman, no matter how beautiful she is. 
    This is general in meaning and includes all mushrik women. The verse in 
    Soorat al-Maa'idah is more specific and permits marriage to women of the 
    people of the Book, as Allaah says: “(Lawful 
    to you in marriage) are chaste women from the believers and chaste women 
    from those who were given the Scripture (Jews and Christians) before your 
    time” [al-Maa’idah 5:5]…  
Then Allaah mentions the 
    wisdom behind the prohibition on the marriage of a Muslim man or woman to 
    one whose beliefs differ from theirs, as He says: “Those (Al-Mushrikoon) 
    invite you to the Fire” i.e., by their words, actions and circumstances, 
    and the one who mixes with them faces danger from them. The danger is not in 
    any worldly sense; rather the danger is eternal doom. End quote. 
If this friend of yours 
    is in a haraam relationship, then you must explain to him that this 
    relationship is haraam and that it is not permissible for a Muslim to be 
    alone with a non-mahram woman, or to shake hands with her or correspond with 
    her, and that he cannot end this relationship by getting married because it 
    is haraam to marry apostate women. He should look for a wife who is 
    religiously committed and can help him to protect his religious commitment 
    and to obey his Lord, and whom he can trust with his children. 
And Allaah knows best.