From Sahih Bukhari (Hadith 7380):
Narrated Masruq:`Aisha said, "If anyone tells you that Muhammad has seen his Lord, he is a liar, for Allah says: 'No vision can grasp Him.' (6.103) And if anyone tells you that Muhammad has seen the Unseen, he is a liar, for Allah says: "None has the knowledge of the Unseen but Allah
Reference: Bukhari 7380