Is a man's giving a gift to his friend's wife considered a form of cuckoldry (dayyūthah) and an opening to discord (fitnah), taking into account that the Messenger of Allah, peace and blessings be upon him, gave gifts to Khadijah's friends after her death, and Mu'awiyah gave a gift to 'Aisha, may Allah be pleased with them both?

It is permissible for a man and a woman who is not his محرم to exchange gifts, unless the purpose of the gift is forbidden or it will lead to fitna (temptation/strife). The Prophet, peace and blessings be upon him, gave gifts to the friends of Khadijah, may Allah be pleased with her, just as Mu'awiyah gave a gift to 'Aishah, may Allah be pleased with her.