Ruling on shaking hands with one’s mother’s maternal aunt
Question

                What is the ruling on greeting my mother’s maternal aunt?.
Praise be to Allah.Your mother’s maternal 
    aunt is also a maternal aunt for you. And you are a mahram for her, so there 
    is nothing wrong with your shaking hands with her. 

    Allaah says, explaining who is a mahram (interpretation of 
    the meaning): 

    “Forbidden to you (for marriage) are: your mothers, your 
    daughters, your sisters, your father’s sisters, your mother’s sisters…”

    [al-Nisa’ 4:23]

    The word khaalah (mother’s sister or maternal aunt) in 
    the verse includes the maternal aunt of one's father and mother, and 
    grandfathers and grandmothers, and the same applies to paternal aunts. 

    Al-Sa’di said (p. 244): 

    ‘Ammah (paternal aunt) refers to the sister of your 
    father and grandfather, no matter how far the line of ascent reaches, and 
    khaalah (maternal aunt) refers to the sister of your mother and 
    grandmother, no matter how far back the line of ascent reaches. End quote. 
    See also Tafseer al-Qaasimi, 5/86 

    It says in Zaad al-Mustaqni’, when discussing which 
    woman are mahrams: Every paternal aunt and maternal aunt, no matter how far 
    back they go. 

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in 
    his commentary: “No matter how far back they go” means the maternal and 
    paternal aunts of one's father, or the maternal or paternal aunts of one’s 
    mother, or the maternal aunt of one's grandmother, or the paternal aunt of 
    one’s grandfather or grandmother, and so on ad infinitum. End quote from 
    al-Sharh al-Mumti’, 5/184.