It is narrated from Ibn Abbas (may Allah be pleased with them both) that he said regarding the man who, after marriage, was alone with his wife but did not have intercourse, and then divorced her, that half of the dowry is obligatory upon him, because Allah Almighty says: "And if you divorce them before you have touched them, and you have appointed for them a dowry, then give half of what you appointed" (Al-Baqarah: 237).
Hadith Referenceمسند الإمام الشافعي / كتاب الطلاق / 1274