Reference: Fataawa Noor ‘alad-Darb – Question No.5811, Page 249, Volume 11
Question: Noble Shaykh, is it permissible for me to go with my sister’s husband in his car, when he picks me up on my visit to my sister’s house; bearing in mind that my sister’s husband asks about me and chats with me, so is it permissible for me to go with him [in his car]?
Response: If there is another [person] with you, such as your sister [herself], or any other person – and [with the condition that] your sister’s husband is trustworthy, then there is no harm [in going with him in his car]. If, however, he is by himself, then this will be [considered as] seclusion, and the Prophet ﷺ has prohibited the seclusion of a man with a woman for whom he is not a mahram.
