Praise be to Allah.
Firstly:
The Muslim, man or woman, should not live in a non-Muslim country unless they fulfil the conditions which make that permissible. That is more emphatically forbidden in the case of a Muslim woman, if she is travelling without a mahram, because staying there poses many dangers to faith and moral conduct.
For more information, please see the answer to question no. 27211 .
Secondly: if the owner of the property has stipulated that the renter should live there by himself, and no one else should live with him, then he is obliged to fulfil that condition.
That is because Muslims are obliged to fulfil contracts and promises. Allah, may He be exalted, says (interpretation of the meaning): {O you who have believed, fulfill [all] contracts} [al-Maa’idah 5:1]. It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawood (3594); classed as saheeh by al-Albaani in Saheeh Abi Dawood.
If the contract does not forbid hosting someone, then you can host her for a while until she puts her affairs in order and is able to look for another place to live.
You can ask the owners of the flat for permission, and tell them about that so as to avoid causing any problems.
And Allah knows best.
Comment