Musnad Ahmad 30:832

Ishaq ibn Yusuf, who is al-Azraq, narrated to us, 'Awf informed us, from Shahr ibn Hawshab, from Abu Hurayrah, he said: I heard him saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "If knowledge were at the Pleiades, men from the sons of Persia would reach it."