What is the prescribed punishment of someone who commits unlawful sexual intercourse with his stepmother? Should he be executed or receive 100 lashes, knowing that this young man is not Muhsan (currently or previously married)?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The majority of scholars hold the view that whoever has had unlawful sexual intercourse, may Allaah guard us against that evil, with his stepmother or the like of his Mahram (unmarriageable kin) women is like the one who does this with a foreign woman in terms of the corporal punishment that he deserves in the worldly life, which is100 lashes if he is not Muhsan or stoning if he is Muhsan.

Some scholars maintain that he should be executed in both cases (i.e. whether he is Muhsan or not). They substantiated their opinion with the Hadeeth that was narrated by Ibn ‘Abbaas in which the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever has sexual intercourse with an unmarriageable woman, kill him.”  [Ahmad, Al-Haakim and Abu Daawood]

The most preponderant opinion is that of the majority of scholars, given the general indication of the verse because the Hadeeth is weak and cannot serve as authentic proof to specify the generality of the verse.

 Allaah Knows best.