Untying the knots and exposing the face of the deceased when burying him
Question

                What is the ruling on untying the knots in the grave and exposing the face of the deceased in the grave?.
Praise be to Allah.
    It is mustahabb to untie the knots in the shroud of the 
    deceased after burying him, because they are only tied lest the shroud fall 
    open. Once he has been placed in the grave, they may be undone. 

    Ibn Qudaamah said in al-Mughni (2/191): 

    With regard to undoing the knots at his head and feet, it is 
    mustahabb, because they were tied lest the shroud fall open, but that is no 
    longer a concern once he has been buried. It was narrated that when the 
    Prophet (blessings and peace of Allaah be upon him) placed Nu’aym ibn 
    Mas’ood al-Ashja’i in the grave, he removed the ropes using his teeth. And a 
    similar report was narrated from Ibn Mas’ood and Samurah ibn Jundub. End 
    quote. 

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in
    Majmoo’ Fataawa Ibn ‘Uthaymeen (17/183): With regard to undoing the 
    knots in the wrappers, there is a report concerning that from ‘Abd-Allaah 
    ibn Mas’ood (may Allaah be pleased with him) who said: When you have placed 
    the deceased in the grave, undo the knots. 

    With regard to uncovering the face of the deceased 
    altogether, there is no basis for that. The most that has been narrated 
    concerning it -- if it is saheeh – is that ‘Umar ibn al-Khattaab (may Allaah 
    be pleased with him) said: When I die and you place me in my grave, let my 
    cheek touch the ground. End quote. 

    And Allaah knows best.