Musnad Ahmad 788:32

Waki’ narrated to us, Yunus bin Abi Ishaq and Ishaq bin Yusuf narrated to us, Yunus bin Abi Ishaq informed us, from Abu Burdah, from Abu Musa, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The orphan girl shall be asked for permission regarding herself. If she remains silent, then that is her permission; and if she refuses, she shall not be coerced."