In regard to the incident that led him to studying Saheeh Bukhaari, Abu Zaid (rahimahullah) mentions:
I was once asleep in the area between the Hajar-e-Aswad and the Maqaam-e-Ebrahim when I had a dream. In the dream, Rasulullah (sallallahu ‘alaihi wasallam) addressed me and said, “O Abu Zaid! How much longer will you study the kitaab of Imaam Shaafi’ee (rahimahullah)? Why do you not study my kitaab?” I immediately asked, “O Rasul of Allah (sallallahu ‘alaihi wasallam)! Which is your kitaab?”
Rasulullah (sallallahu ‘alaihi wasallam) replied, “The kitaab of Muhammed bin Ismaa’eel Bukhaari (rahimahullah).”
(Siyar A’laamin Nubalaa 12/438)