Every major authenticated hadith about zina — the prohibition, the consequences, the pathways, and the mercy of tawbah — from Bukhari, Muslim, and the major hadith collections.
The Prophet Muhammad ﷺ addressed zina in multiple contexts, from the abstract (the seven types) to the practical (what leads to it, how to avoid it, and what to do after it). These hadith together form the most complete practical guide to sexual ethics in any religious tradition.
"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 hands is touching, the zina of the feet is walking (toward it), and the heart desires and longs — the private parts then confirm or deny all of this." — Bukhari 6243, Muslim 2657
"The fornicator does not commit fornication while he is a believer (in a complete state of iman)." — Bukhari 2475, Muslim 57
"When fornication and usury become widespread in a community, they have invited upon themselves the punishment of Allah." — Al-Hakim, graded authentic by Al-Albani
"O Ali, do not follow one look with another — the first is permitted, the second is not." — Tirmidhi 2777
"The (unlawful) look is an arrow from Iblis's arrows." — Al-Hakim, authentic
"Let no man be alone with a woman — for the third of them is Shaytan." — Tirmidhi 2165, graded sahih
"O young people, whoever can marry, let him marry — it lowers the gaze and guards chastity. Whoever cannot, let him fast — it is a shield." — Bukhari 5066, Muslim 1400
"Allah is more delighted at the repentance of His servant than one of you at finding your lost mount in a desert." — Bukhari 6309, Muslim 2747
"Why did you not leave him to repent, so that Allah might have accepted his repentance?" — Sahih Muslim 1695 (on Ma'iz's case)