Why was there no verse explicitly prohibiting adultery, but rather a mere prohibition, and on what basis is a married fornicator stoned to death despite the absence of a Quranic verse to that effect?

Transforming definitive matters into probabilistic ones, and turning consensus into disputed issues, is considered one of the greatest tribulations. The prohibition of zina (fornication/adultery) is a matter of consensus, and it is known by necessity to be part of the religion, just like the obligation of prayer and the prohibition of alcohol. Whoever denies something known by necessity to be part of the religion commits kufr (disbelief). The prohibition of zina is established by the Holy Quran, the Prophetic Sunnah, scholarly consensus (ijma'), and the general principles of Islamic Law. Immoral acts (fawahish) are prohibited by the text of the Quran, and zina is an immoral act. The Prophetic hadiths clarify the punishment for zina and its gravity, and demonstrate the Sunnah's role in interpreting the Quran. Muslim scholars have unanimously agreed on the prohibition of zina, and it is known by necessity to be part of the religion. The general principles of Islamic Law indicate its prohibition due to the harm it inflicts upon the individual and society.