Musannaf Ibn Abi Shayba 33:756

Waki’ narrated to us, from Sufyan, from Abu Hayyan, from Abu al-Zanba’, from Abu al-Dihqan, who said: While a young man was walking with al-Ahnaf, he said to him: "O son of my brother, if the truth is presented to you, then aim for it, and be heedless of whatever is besides it."