Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said concerning the saying of Allah Almighty: "Let those whom your right hands possess and those of you who have not reached puberty ask your permission three times" [Surah al-Nur: 58]: When a man is alone with his wife after the Isha prayer, no servant and no child should enter without permission until the morning prayer has been offered; and when he is alone with his wife at midday, it is the same. Then permission was given for them to enter without permission in the time between these, under the saying of Allah: "There is no blame on you or on them after these (times)" [Surah al-Nur: 58]. As for one who has reached puberty, he should not enter upon a man and his wife without permission under any circumstances, because Allah says: "And when the children among you reach puberty, let them ask permission" [Surah al-Nur: 59].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13553