Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said about a man who, after marrying, was alone with his wife but divorced her before consummation: He must pay half the dowry, because this is the command of Allah: "And if you divorce them before you have touched them, while you have already fixed a dowry for them, then (pay) half of what you fixed" [Surah al-Baqarah: 237].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14473