Does engaging in sexual acts with a married woman online only constitute zina (adultery/fornication), and is it obligatory to inform her husband to seek his permission or forgiveness?

The Sharia has designated some words and actions as Zina (fornication/adultery), such as looking, listening, speaking, touching, walking, and the heart desiring, based on what Al-Bukhari and Muslim narrated from Abu Hurayrah that the Prophet (peace be upon him) said: "The son of Adam has his share of Zina written for him, which he will inevitably attain. The Zina of the eyes is looking, the Zina of the ears is listening, the Zina of the tongue is speaking, the Zina of the hand is touching, and the Zina of the foot is walking. The heart desires and wishes, and the private part confirms or denies that."

These actions are not the actual Zina that necessitates a prescribed punishment (Hadd), but their designation as Zina indicates their seriousness because they are a means to actual Zina. This falls under the principle of blocking the means (Sadd al-Dhara'i'), in fulfillment of Allah's saying: "And do not approach unlawful sexual intercourse. Indeed, it is ever an indecency and an evil way." (Quran 17:32).

The sin becomes graver if the woman is married, due to the transgression against her husband's honor. One must hasten to sincere repentance (Tawbah Nasuh). It is not obligatory to inform the husband of this; rather, it suffices to frequently supplicate for him and seek forgiveness. One must be cautious of leniency in dealing with women, as it is established in the Sahihayn from Usama bin Zayd (may Allah be pleased with them both) that the Prophet (peace be upon him) said: "I have not left behind me a trial more harmful to men than women." And in Sahih Muslim, from Abu Sa'id Al-Khudri (may Allah be pleased with him), the Prophet (peace be upon him) said: "Indeed, this world is sweet and green, and indeed Allah is going to make you vicegerents in it, and He will see how you act. So, beware of the world and beware of women, for the first trial of the Children of Israel was concerning women."