Sahih Bukhari Volume 006, Book 060, Hadith Number 061.
Narrated By Abu Huraira : Allah's Apostle said, "We have more right to be in doubt than Abraham when he said, 'My Lord! Show me how You give life to the dead.' He said, 'Do you not believe?' He said, 'Yes (I believe) but to be stronger in Faith.'" (2.260)