Musnad Abu Ya'la al-Mawsili 107:4

Zuhayr narrated to us, Ma'n ibn 'Isa narrated to us, Mu'awiyah ibn Salih narrated to us, from Buhayr ibn Sa'd, from Khalid ibn Ma'dan, from Kathir ibn Murrah, from 'Uqbah ibn 'Amir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The one who recites the Quran secretly is like the one who gives charity secretly, and the one who recites the Quran openly is like the one who gives charity openly."