Musnad Ahmad 1017:118

Waki' narrated to us, 'Uyaynah ibn 'Abd al-Rahman narrated to us, from his father, from Buraydah al-Aslami, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You must follow a moderate path, for whoever contends with this religion will be overcome by it."