حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرِ بْنِ حَزْمٍ، ‏.‏ أَنَّ فِي الْكِتَابِ الَّذِي، كَتَبَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم لِعَمْرِو بْنِ حَزْمٍ ‏"‏ أَنْ لاَ يَمَسَّ الْقُرْآنَ إِلاَّ طَاهِرٌ ‏"‏ ‏.‏

Yahya related to me from Malik from Abdullah ibn Abi Bakr ibn Hazm that in a letter that the Messenger of Allah, may Allah bless him and grant him peace, sent to Amr ibn Hazm it said that no-one should touch the Qur'an unless he was pure. Translation Not Available

Book reference: Muwatta Imam Malik Book 15 Hadith 473
Web reference: Muwatta Imam Malik Book 15 Hadith 1