It is narrated from Ibn Abbas (may Allah be pleased with them both) that he reports from the Prophet (peace and blessings be upon him) that he said: "Beware! I have been forbidden from reciting the Qur'an while in the state of bowing and prostration. In bowing, glorify the greatness of your Lord, and in prostration, make abundant supplication, for your supplication is more worthy of being accepted."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 225
Hadith Takhrijاخرجه مسلم الصلاة، باب النهي عن قرأة القرآن في الركوع والسجود: 479