Hadith: You have no right over her. The man said: O Messenger of Allah, what about my money? The Prophet (may Allah's peace and blessings be upon him) said: You have no right to get back your money. If you have told the truth about her, then your money was in return for the sexual intercourse you lawfully had with her; and if you have told a lie about her, then you are less rightful to get your money back

عن عبد الله بن عمر رضي الله عنهما مرفوعاً: «أن فلان بن فلان قال: يا رسول الله، أرأيت أن لو وجد أحدنا امرأته على فاحشة، كيف يصنع؟ إن تكلم تكلم بأمر عظيم، وإن سَكَتَ سَكَتَ على مثل ذلك. قال: فسكت النبي صلى الله عليه وسلم فلم يُجبه. فلما كان بعد ذلك أتاه فقال: إن الذي سألتك عنه قد ابتليت به. فأنزل الله عز وجل هؤلاء الآيات في سورة النور ?والذين يرمون أزواجهم...? فتلاهن عليه ووعظه وذكره. وأخبره أن عذاب الدنيا أهون من عذاب الآخرة. فقال: لا، والذي بعثك بالحق، ما كذبتُ عليها. ثم دعاها، فوعظها، وأخبرها: أن عذاب الدنيا أهون من عذاب الآخرة. فقالت: لا، والذي بعثك بالحق، إنه لكاذب. فبدأ بالرجل؛ فشهد أربع شهادات بالله: إنه لمن الصادقين، والخامسة: أن لعنة الله عليه إن كان من الكاذبين. ثم ثَنَّى بالمرأة. فشهدت أربع شهادات بالله: إنه لمن الكاذبين، والخامسة: أن غضب الله عليها إن كان من الصادقين. ثم فرق بينهما. ثم قال: إن الله يعلم أن أحدكما كاذب فهل منكما تائب؟ -ثلاثا-»، وفي لفظ «لا سبيل لك عليها. قال: يا رسول الله، مالي؟ قال: لا مال لك: إن كنت صدقت عليها فهو بما استحللت من فرجها، وإن كنت كذبت فهو أبعد لك منها».
[صحيح] - [متفق عليه]

‘Abdullāh ibn ‘Umar (may Allah be pleased with him) reported: So-and-so came and asked: "O Messenger of Allah, if one of us finds his wife committing adultery: what should he do? If he were to speak, his statement would be a horrible matter, and if he were to remain silent, his silence about the matter would be horrible too." The Messenger of Allah (may Allah's peace and blessings be upon him) remained silent. After some time, the man came back to the Messenger of Allah (may Allah's peace and blessings be upon him) and said: "I have become afflicted by the very thing I asked you about." Then Allah, the Exalted, revealed these verses of Sūrat An-Nūr (which begins with): {And those who accuse their wives} [Sūrat- An-Nūr: 6]. The Prophet (may Allah's peace and blessings be upon him) recited them to him. Then he admonished him, exhorted him, and informed him that the torment of this world is less painful than the torment of the Hereafter. The man said: "No, by the One Who sent you with the Truth, I did not tell a lie against her." The Prophet (may Allah's peace and blessings be upon him) then called the wife and admonished her, exhorted her, and informed her that the torment of this world is less painful than the torment of the Hereafter. She said: "No, by the One Who sent you with the Truth, he is a liar." The Prophet (may Allah's peace and blessings be upon him) started with the man, who testified in the name of Allah four times that he was truthful, and the fifth time, he said: "Let Allah's curse fall upon me if I am a liar." Then the woman was summoned, and she testified four times by the name of Allah that her husband was among the liars, and the fifth time, she said: "Let the anger of Allah fall upon me if he is truthful." Then the Prophet (may Allah's peace and blessings be upon him) separated them and said: "Indeed, Allah knows that one of you is a liar, so would any of you repent?" He said this statement thrice. According to another wording of the Hadīth, the Prophet (may Allah's peace and blessings be upon him) said: "You have no right over her." The man said: "O Messenger of Allah, what about my money?" The Prophet (may Allah's peace and blessings be upon him) said: "You have no right to get back your money. If you have told the truth about her, then your money was in return for the sexual intercourse which you lawfully had with her, and if you have told a lie about her, then you are less rightful to get your money back."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Islam legislated the law of 'Li‘ān' (invoking the curse of Allah upon the liar among the two spouses for falsehood in the matter of witnessing adultery) as a solution to the problem of a husband witnessing another man committing adultery with his wife without four other witnesses (or visa versa). The husband cannot just be in suspicion about the matter: he must clearly witness the actual act of penetration of the adultery. The punishment for any false accusation and lying in this matter is extremely grievous (torment in Hellfire). The man in this story was feeling doubtful about the conduct of his wife and was worried that she might commit adultery. He was confused about what to do, for if he accused her (without the four witnesses) then he would undergo the relevant legal punishment (of whipping, etc), and if he remained silent about it then he would be considered a cuckold and suffer disgrace. He went to the Prophet (may Allah's peace and blessings be upon him) and mentioned these things to him. The Prophet (may Allah's peace and blessings be upon him) remained silent as he did not like to answer questions about issues which had not yet occurred, because this leads to evil and could possibly open the doors for evil to occur. In addition to that no verses were yet revealed to the Prophet (may Allah's peace and blessings be upon him) regarding this issue. After some time the same man who questioned the Prophet (may Allah's peace and blessings be upon him) saw the monstrosity (adultery) he had asked about previously and about which he had worries. Thereupon Allah revealed some rulings regarding this issue in Sūrat An-Nūr, as He says (what means) {Those who accuse their wives} [Qur'an 24:6]. The Prophet (may Allah's peace and blessings be upon him) recited these verses to the man, admonished him and reminded him that if he was lying in accusing his wife, then the worldly punishment of false accusations is less severe than the punishment of the Hereafter. The man swore the sacred oath by Allah that he was not lying about witnessing and accusing his wife of adultery. Then the Prophet (may Allah's peace and blessings be upon him) called the wife and admonished her and told her that the punishment of this life is less severe than the punishment of the Hereafter. Then she swore also that her husband was a liar. Then, the Prophet may Allah's peace and blessings be upon him, started by the one with whom Allah has started with (i.e. in the Qur'anic verses mentioned above), the husband. The man testified four times by Allah that he was truthful in what he accused his wife with, and upon the fifth time he invoked the curse of Allah upon himself if he was a liar. Then the Prophet (may Allah's peace and blessings be upon him) summoned his wife, and she testifies four times by Allah that her husband was a liar, and she also upon the fifth time invoked the anger of Allah upon herself if her husband was truthful. Then the Prophet (may Allah's peace and blessings be upon him) separated between them permanently (and irrevocably). Given that one of them was definitely a liar, the Prophet (may Allah's peace and blessings be upon him) urged them to repent. Then the husband requested his dowry back and the Prophet (may Allah's peace and blessings be upon him) said: "you have no right to claim the dowry: if you were truthful about her committing adultery then the dowry you gave her was in exchange for your sexual relations with her during your marriage. And if you were lying about her, then it is even less rightful that you would receive anything because you accused her of such a terrible lie and great falsehood.