Hadith: When Mā‘iz ibn Mālik came to the Prophet (may Allah's peace and blessings be upon him) (in order to confess adultery), the Prophet (may Allah's peace and blessings be upon him) said to him: Probably you have only kissed, winked, or looked (at the lady)? He said: No, O Messenger of Allah. The Prophet (may Allah's peace and blessings be upon him) said: using no euphemism: Did you copulate with her? The narrator added: At that, (i.e. after his confession) the Prophet (may Allah's peace and blessings be upon him) ordered that he be stoned (to death)

عن ابن عباس رضي الله عنهما قال: لما أتى ماعزُ بن مالك النبيَّ صلى الله عليه وسلم قال له: «لعلك قَبَّلْتَ، أو غَمَزْتَ، أو نَظَرْتَ» قال: لا يا رسول الله، قال: «أَنِكْتَهَا». لا يَكْنِي، قال: فعند ذلك أَمَرَ بِرَجْمِهِ.
[صحيح] - [رواه البخاري]

Ibn ‘Abbās (may Allah be pleased with him) reported: When Mā‘iz ibn Mālik came to the Prophet (may Allah's peace and blessings be upon him) (in order to confess adultery), the Prophet (may Allah's peace and blessings be upon him) said to him: "Probably you have only kissed, winked, or looked (at the lady)?" He said: "No, O Messenger of Allah." The Prophet (may Allah's peace and blessings be upon him) said: using no euphemism: "Did you copulate with her?" The narrator added: "At that, (i.e. after his confession) the Prophet (may Allah's peace and blessings be upon him) ordered that he be stoned (to death)."
Sahih/Authentic. - [Al-Bukhari]

Explanation

This Hadīth is about the story of Mā‘iz (may Allah be pleased with him) who went to the Prophet (may Allah's peace and blessings be upon him) to confess that he had committed adultery. Initially, the Prophet (may Allah's peace and blessings be upon him) wanted to verify his sanity, the validity of his confession, and whether or not he precisely understood what adultery meant. This was because he might have committed some introductory acts of adultery that would not amount to the crime of adultery itself, but thought that such acts were considered adultery. Therefore, the Prophet (may Allah's peace and blessings be upon him) first asked him about kissing, winking and the like. When the Prophet (may Allah's peace and blessings be upon him) verified that Mā‘iz knew what real adultery was, he ordered him to be stoned to death after verifying the validity of his confession.