[4:15] As for those of your women who commit lewdness, call four of you to witness against them; and if they witness, then detain them in their houses until death take them or God appoints for them a way.
Verily He made allowances in proving lewdness, which is fornication, for an excessive amount of witnessing, in order to lower the veil of generosity over the sins of servants. Indeed, the establishment of the act of witnessing in the way in which it exists in the law for proving this situation is like the one who pleads for the defense.
In [the Prophet's words] (ṣ) when Māʿiz ibn Mālik said to him, 'O Messenger of God, may the blessings of God be upon you, I have fornicated', he said: Maybe you kissed? Other times he said: Smell his breath. There is the strongest proof in this of what I have mentioned of the lowering of the veil over ugly acts.