It is only Allah who knows the secrets of the hearts.
It comes in the holy Qur'an,

Say: ‘No one in the heavens and the earth knows the unseen except Allah.’ They are not aware of when they will be raised. (Surat an-Naml, 65).

The keys of the unseen are in His possession. No one knows them but Him… (Surat al-An’am, 59)


The prophet (s.a.w) does not have the knowledge of what is in the hearts. Whatever he knew was through dis-closer from his Lord. Allah addresses him in the holy Qur'an at several occasions

This is news of the unseen which We reveal to you. You were not with them when they decided what to do and devised their scheme. (Surah Yusuf, 102)

This is news from the unseen which We reveal to you. You were not with them when they cast their reeds to see which of them would be the guardian of Maryam. You were not with them when they quarrelled. (Surah Al ‘Imran, 44)

The Prophet confided a certain matter to one of his wives, then when she divulged it Allah disclosed that to him, and he communicated part of it and withheld part of it.When he told her of it, she said, “Who told you of this?” He said, “The All-Knowing and All-Aware informed me of it.” (Surat at-Tahrim, 3)

In the last ayah we see that the Prophet (s.a.w.) did not know what one of his wives had done. He came to know only when Allah informed him.