Hadith: Beware of entering upon women. A man from the Ansār said: O Messenger of Allah, what about Al-Hamw? He said: Al-Hamw is death

عن عقبة بن عامر رضي الله عنه مرفوعاً: «إياكم والدخولَ على النساء، فقال رجل من الأنصار: يا رسول الله، أرأيتَ الحَمُو؟ قال: الحَمُو الموتُ». ولمسلم: عن أبي الطاهر عن ابن وهب قال: سمعت الليث يقول: الحمو: أخو الزوج وما أشبهه من أقارب الزوج، ابن عم ونحوه.
[صحيح] - [متفق عليه]

‘Uqbah ibn ‘Āmir (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Beware of entering upon (non-Mahram) women." A man from the Ansār said: "O Messenger of Allah, what about Al-Hamw?" He said: "Al-Hamw is death." Imām Muslim narrated from Abu At-Tāhir from Ibn Wahb that he said: "I heard Al-Layth saying: Al-Hamw is the husband's brother and similar male relatives of the husband, such as the husband's cousin and the like."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

The Prophet (may Allah's peace and blessings be upon him) warns men from entering upon non-Mahram women and staying in seclusion with them. (As mentioned in a Hadīth) never is a man alone with a woman but the devil is their third. By nature human souls are weak and the motivations to sin are strong, and therefore this can lead to committing the unlawful. The Prophet forbade Muslim men from staying in seclusion with a non-Mahram woman to ward off evil temptations and the means to anything unlawful. Then a man said: Tell us, O Messenger of Allah, about the husband's male relative (Al-Hamw), for perhaps he might need to enter the house of his relative, the husband, while the wife is alone inside. Does this person have a concession to enter? The Prophet (may Allah's peace and blessings be upon him) answered: "Al-Hamw is death," meaning that entering the house while the husband is away is extremely destructive because people have grown accustomed to letting the husband's male relatives enter even if the husband is away. Since this is customary and is not denounced practice ends up alone with a woman who is not his Mahram leading to temptations to sin and possibly a secret affair that no one suspects. Consequently this would become destruction of their religion and eternal punishment. Upon this basis the ruling is that the husband's male relatives have no concession to enter upon the wife in seclusion, and Muslims should beware of their private seclusion with your women if you have any sense of protection and jealousy.