Is it permissible for a group of girls to stay overnight in the mosque (“sleepover”)?
Question

                I live in Denmark, we have a kinda of musalah or a majid in a lokal town and my question is about, can girls overnight in the majid without a muhram. The reason these girls are overnighting in majid is, to spend time with each other and to speak about islamic things and benefit each other. Though they are sleeping there without a muhram they have permission from their parents/muhrams. And this majid/musalah is saparated from the mens majid but they are still close.(so they can be heard if they are to load or they can be seen of the men just come in their side on purpose).
Praise be to Allah.
    Islam does not stipulate that a woman should have a mahram 
    with her except in the case of travel. If she wants to go to the mosque or 
    the marketplace or to visit a neighbour or relative, and the place is nearby 
    and the one who goes there is not regarded as being a traveller, then there 
    is nothing wrong with her going there on her own without a mahram. But it is 
    stipulated that the place should be safe, so the route should be safe with 
    no danger to her as she comes and goes. 

    If the route is safe and the girl can reach the mosque, there 
    is nothing wrong with her meeting with her sisters to do some communal 
    actions such as seeking knowledge, or individual actions such as reading 
    Qur’aan and praying. As for staying overnight in the mosque with her friends 
    and sisters, it is permissible in principle if the women’s prayer space is 
    secure and safe from men entering it or from the foolish trying to overstep 
    the mark with them. That is a matter to be weighed up by the people in 
    charge of the mosque, namely the administration, the imam and the committee 
    that looks after it, as well as parents. Every environment has its own 
    rulings. The most important thing is that the girls should be safe from men 
    entering upon them and the foolish trying to overstep the mark with them. It 
    is preferable for there to be someone who can take charge and take care of 
    them, such as a woman who is a seeker of knowledge (taalibat ‘ilm), so that 
    no fitnah will result from their gathering and so as to make sure they 
    behave themselves in accordance with Islamic guidelines and do not waste 
    their time. 

    Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allah have 
    mercy on him) said: Women may observe i‘tikaaf so long as no fitnah results 
    from their doing so. If it will result in fitnah, then they should not be 
    allowed to do that, because if something that is mustahabb will result in 
    something that is forbidden, it must be prevented, just as if something that 
    is permitted will result in something that is forbidden, it must be 
    prevented… 

    … But it may be said: How can (a woman) observe i‘tikaaf in a 
    mosque in which prayers in congregation are not held? Is that not a source 
    of fitnah? 

    The response is that it may or may not be so. This mosque may 
    be safe and secure, and no one enters it, so there is no fear of fitnah for 
    the women if they observe i‘tikaaf there. Or it may be the opposite. The 
    point is that if fitnah will occur, the women should not be allowed to 
    observe i‘tikaaf, no matter which mosque it is. 

    End quote from ash-Sharh al-Mumti‘ Zaad al-Mustaqni‘, 
    6/510, 511 

    It is not permissible for women to raise their voices to the 
    extent that they may be heard by men. If women are forbidden to say tasbeeh 
    (“Subhaan Allah”) to alert the imam if he makes a mistake in the prayer, and 
    they are forbidden to give the adhaan (call to prayer), lead the prayer and 
    deliver the khutbah (sermon), all of which involve dhikr or remembrance of 
    Allah, then it is more appropriate that they be forbidden to raise their 
    voices in other kinds of speech. 

    Ibn Hajar (may Allah have mercy on him) Women are forbidden 
    to say tasbeeh (to alert the imam to a mistake in the prayer) because they 
    are enjoined to lower their voices in prayer in general, because of the fear 
    of temptation (fitnah). 

    End quote from Fath al-Baari, 3/77. See also the 
    answers to questions no. 9279 
    and 39186 

    This is as far as the shar‘i ruling is concerned. However we 
    do not advise staying over in the mosque for the purpose mentioned; we think 
    that it is sufficient for the girls to spend the day there, whether that is 
    studying together or worshipping together, then they should go back to their 
    homes at night. 

    We ask Allah to protect them, take care of them and help them 
    to do that which pleases Him. For more information please see the answer to 
    questions no. 49898 and
    26298 

    And Allah knows best.