It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When someone has peeped inside, then there is no permission for him anymore."
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1089
It is narrated from Muslim bin Nazeer (may Allah have mercy on him), he said that a man sought permission from Sayyiduna Hudhaifah (may Allah be pleased with him), so he peeked in and said: "May I come in?" Sayyiduna Hudhaifah (may Allah be pleased with him) said: "Your eye has already entered, only your body remains (so what is the need for permission now?)"
And a man asked: "Should I seek permission even to go to my mother?" He replied: "If you do not seek permission, you may see something that you would dislike to see."
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1090
Hadith Gradingالألبانی:صحيح ، حسن
Hadith Takhrij«صحيح ، حسن : أخرجه ابن أبى شيبة : 26237 و الخرائطي فى اعتلال القلوب : 281 و أخرجه عبدالرزاق : 19421 و البيهقي فى الكبرىٰ : 97/7»
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that a Bedouin came to the house of the Messenger of Allah (peace and blessings of Allah be upon him) and looked inside through a hole in the door. The Messenger of Allah (peace and blessings of Allah be upon him) picked up an arrow or a spear to poke out the Bedouin’s eye, so he moved back. The Prophet (peace and blessings of Allah be upon him) said: “If you had remained standing, I would certainly have poked out your eye.”
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1091
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه النسائي ، كتاب القسامة : 4862 و هو فى الكبرىٰ : ح : 7063»
It is narrated from Sayyiduna Umar bin Khattab (may Allah be pleased with him), he said: Whoever deliberately looked fully into a house before being granted permission has committed a sin.
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1092
Hadith Gradingالألبانی:ضعيف الإسناد موقوفًا
Hadith Takhrij«ضعيف الإسناد موقوفًا : أخرجه البيهقي فى شعب الإيمان : 8828»
The freed slave of the Prophet (ﷺ), Sayyiduna Thawban (may Allah be pleased with him), narrated that the Prophet (ﷺ) said: "It is not lawful for any Muslim man to peep into a house before seeking permission; if he does so, he has entered without permission. And when a person leads the prayer, he should not make a special supplication for himself before finishing the prayer (rather, he should include the followers in every supplication), and no person should pray while restraining urine or feces, until he relieves himself."
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1093
Hadith Gradingالألبانی:صحيح دون جملة الإمامة
Hadith Takhrij«صحيح دون جملة الإمامة : أخرجه أبوداؤد ، كتاب الطهارة : 90 و الترمذي ، الصلاة : 357»