Musnad Ahmad 30:3287

Ishaq ibn Isa narrated to us, he said: Jarir—meaning Ibn Hazim—narrated to us, from al-Zubayr ibn al-Khirrit, from Ikrimah, from Abu Hurayrah, who said: "The Messenger of Allah, may Allah bless him and grant him peace, decreed that when people disagree regarding their roads, they shall be seven cubits."