What is the ruling on joking with a girl with whom one is safe from temptation in all situations, and what prevents joking and friendship with a girl if she is ugly, if the reason for prohibiting friendship with a girl is temptation?

The religious texts that command women to observe hijab and avoid unrelated men include all women. The reason and wisdom behind these rulings are not the presence of lust, but the fear of fitna (temptation/strife). Sheikh al-Islam Ibn Taymiyyah stated that looking at the face of an unrelated woman without necessity is impermissible, even if lust is absent, for fear of arousing it. This is why khalwa (private seclusion) with an unrelated woman is forbidden, as it is a place prone to fitna. The principle is that anything that leads to fitna is impermissible. It is also impermissible to accompany or joke with an unrelated woman, even if she lacks beauty, because a woman is a source of fitna, both for others and for herself. The jurists have broadly prohibited accompanying an unrelated woman, without excluding the ugly or the young, because fitna is common, and just as one fears being tempted by her, one fears being tempted by him. Therefore, it is not permissible for unrelated men and women to accompany each other due to the door it opens to fitna and corruption.