My sister is suffering because of her husband; can I advise her to seek a divorce?
Question

My sister’s husband is foul-mouthed; he reviles and berates her in the worst of phrases, beats her and always threatens to kill her and threatens to harm my older brother for no reason. He causes trouble for no reason, like one who is mentally disturbed. Please note that she is the one who spends on him and on the house, as she pays for rent, food and clothing. She has five children, and he is unemployed; he does not want to work even though he is in good health. Is it permissible to advise her to seek a divorce from him, because she fears for her life and the life of her children, or does this come under the heading of creating troubles between spouses?
Praise be to Allah.Firstly:
If the situation is as described in the question, undoubtedly this is one of the troubles of life. It is not appropriate for a man whom Allah has enjoined to be in charge of his household, spend on them and shoulder the responsibility of raising his children to be like this. The Prophet (blessings and peace of Allah be upon him) said: “Each of you is in a position of responsibility and each of you is answerable for those under his care. A man is in a position of responsibility over his household and is answerable for those under his care. A woman is in a position of responsibility over her husband’s house and children and is answerable for those under her care. Indeed, each of you is in a position of responsibility and each of you is answerable for those under his care.” Narrated by al-Bukhari (2278).
It is well known that the woman has the right to ask for divorce (talaq) or khul‘ if there is a reason for that. It was narrated from Ibn ‘Abbas (may Allah be pleased with him) that the wife of Thabit ibn Qays came to the Prophet (blessings and peace of Allah be upon him) and said: “O Messenger of Allah, I do not find any fault with Thaabit ibn Qays in his character or his religious commitment, but I do not want to commit any act of disbelief after becoming a Muslim.” The Prophet (blessings and peace of Allah be upon him) said to her, “Will you give back his garden [that he had given to her as the mahr]?” She said, “Yes.” So the Messenger of Allah (blessings and peace of Allah be upon him) said to Thaabit: “Take back your garden, and divorce her.” 
What is meant by her words “but I do not want to commit any act of disbelief after becoming a Muslim” is: I do not want to do any actions that are contrary to the rulings of Islam, such as despising my husband, disobeying him, not fulfilling his rights, and so on.
See: Fath al-Bari (9/400).
Shaykh Ibn Jibrin (may Allah have mercy on him) said, explaining what justifies seeking khul‘:
If the woman dislikes her husband’s characteristics, such as if he is harsh, strict, short-tempered, filled with anger, criticizes the slightest action and rebukes her for the slightest shortcoming, then she has the right to seek khul‘.
Secondly: if she dislikes his appearance, such as a flaw, a defect, or a deficiency in his senses, then she has the right to seek khul‘.
Thirdly: if he is lacking in religious commitment, such as if he does not pray or is careless about attending prayers in congregation, or he breaks the fast of Ramadan with no excuse, or he goes to places where haram activities take place, such as zina, drinking, listening to music and entertainment, and the like, then she has the right to seek khul‘.
Fourthly: If he deprives her of her rights, such as maintenance, clothing or essential needs, when he is able to provide those things, then she has the right to seek khul‘.
Fifthly: If he does not give her her right to regular intimacy in a way that will keep her chaste because he is impotent, or has no interest in her, or he prefers someone else, or he is not fair in sharing his time [among co-wives], then she has the right to seek khul‘. And Allah knows best. End quote.
See also the answer to question no. 1859 .
Secondly:
As your sister is the one who is in charge, and she knows her husband’s condition better than anyone, she is the one who should decide whether it is better to stay with him for the sake of the children despite these annoyances, because the presence of the father and the sense of family unity has a positive psychological impact on the children, gives them a good social standing and it helps in giving them a good upbringing, and in many cases it is better than separation.
We should also note that our advice should differ, depending on whether the couple have children or not. Making sacrifices for the sake of the children’s safety, their social standing, their psychological wellbeing and sense of family is worth patience and sacrifice.
She should also persist in calling upon Allah, asking Him to rectify his condition, and she should ask sincere and knowledgeable people to advise him. For hearts fluctuate, and they are in the hand of Allah. How many people have come back to their senses and settled down after having gone astray and misbehaved.
If there is anyone among his family and relatives who is rational and mature in thinking, and is held in high esteem by him and can influence him, then she can seek his help to influence him and tell him about his situation, if there is the hope that this will help to rectify his condition.
What appears to us to be the case is that if your sister shows patience, which is indicative of her rational mind and far-sightedness, no one should interfere by advising her to leave him, which could cause greater harm than the harm that results from her staying with this husband despite the problems he has.
But if she fears for her life, her faith or her children, then let her do that; there is nothing wrong with her seeking separation from him in that case.
And Allah knows best.