Musnad Ahmad 1034:26

Yahya ibn Sa'id narrated to us, from Shu'bah, from Mansur, from 'Abdullah ibn Yasar, from Hudhayfah, from the Prophet, may Allah bless him and grant him peace, who said: "Do not say, 'What Allah wills and what so-and-so wills.' Say, 'What Allah wills, then what so-and-so wills.'"