Abdullah bin Abi Bakr (may Allah have mercy on him) narrates from his father that in the letter of the Prophet (peace and blessings be upon him) to Amr bin Hazm (may Allah be pleased with him) there was: "Touch the Qur'an only while in a state of ablution."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 408
Hadith Gradingمحدثین:صحيح لغيرهٖ
Hadith Takhrij«صحيح لغيرهٖ۔ أخرجه الدار قطني 1/121»