Is there a contradiction between the Hadith from which it is understood that a man is permitted to kill his wife if he sees her with another man, and the Hadith in which the Prophet (peace be upon him) commands that four witnesses be brought in the same situation?

There is an apparent contradiction in the two hadiths of Sa'd, and the problematic aspect is: "Are you astonished by Sa'd's jealousy?" This affirmation has been used by those who permitted what Sa'd did, saying: if that occurred, the killer's blood would be shed with impunity.

The correct view is that jealousy does not permit the jealous person to do what is forbidden to him. He must submit to the حكم of Allah and His Messenger and not overstep his bounds. The hadith indicates the obligation of retribution (qisas) for someone who kills a man he found with his wife, because Allah has obligated witnesses for punishments (hudud), and it is not permissible to transgress Allah's limits or shed blood based on a mere claim.

This hadith serves to block pretexts and prevent chaos that could lead to people being killed and falsely accused in such matters. It also prohibits the implementation of punishments without authority or witnesses.

This is the view of the majority of scholars, for the blood of a Muslim is sacred and may not be shed except by what Allah has permitted with clear evidence. This is what Ali ibn Abi Talib ruled, and it is also what is narrated from Al-Shafi'i. Allah has forbidden the shedding of believers' blood except by right, and the Prophet forbade Sa'd from killing until he brought four witnesses, which indicates the prohibition of killing anyone without clear evidence.