What is the ruling of Islamic law on following the fatwa of the Egyptian Dar al-Ifta that divorce does not occur and that an expiation for an oath is due for one who swore "by divorce I did not take anything" while he is a liar, knowing that the mufti did not inquire about the intention?

There is no blame on someone who acts upon the fatwa of a trusted scholar in a disputed matter. Some scholars, including Ibn Taymiyyah, held that if someone swears by divorce falsely, his wife is not divorced, and he is not required to offer an expiation for an oath. Therefore, there is no blame on you for acting upon the fatwa of the Dar al-Ifta that the divorce did not occur. However, you must repent to Allah for intentionally lying and be cautious of swearing by divorce, as it is among the oaths of the wicked.