What is the expiation for incomplete fornication?

It is reported in the Sahihayn from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The son of Adam has his share of adultery decreed for him, which he will inevitably attain. The adultery of the eyes is looking, and the adultery of the ears is listening, and the adultery of the tongue is speaking, and the adultery of the hand is touching, and the adultery of the foot is walking. The heart desires and wishes, and the private part either confirms or denies that." The expiation for these sins is sincere repentance to Allah and seeking forgiveness, which includes abstaining from the sin, regretting it, and resolving not to return to it. For repentance to be accepted, it must be before the death rattle and before the sun rises from the west. It should be followed by righteous deeds that erase evil deeds and replace them with good ones.

As for the prescribed punishment mentioned in the verse: "The adulteress and the adulterer, lash each one of them with a hundred lashes," this is for those who commit aggravated adultery. As for the مقدمات (preliminaries) of adultery, they are subject to discretionary punishment (ta'zeer) according to the judge's discretion. In summary, the expiation for these matters is sincere repentance and an abundance of good deeds.