Sayyiduna Ibn Abbas (may Allah be pleased with them both) used to say: There is a verse in which most people do not believe (i.e. they do not act upon it): the verse of permission. And I order even this slave-girl of mine (a short slave-girl of his who was standing by his head) to ask permission before coming in to me.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13555