Musannaf Ibn Abi Shayba 13:3074

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Al-Muthanna ibn Sa’id al-Duba’i narrated to us, from Qatadah, from Bashir ibn Ka’b, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Make the road seven cubits."