The Heart [fuaad] Lied not in what he saw [Najm 53:11]

مَا كَذَبَ الْفُؤَادُ مَا رَأَىٰ

“The (Prophet’s) heart lied not in what he saw.” (Surah Najm 53:11)
The fu’aad is the heart, and this means that the what the Prophet (sal Allahu alayhi wa sallam) saw with his eyes during the night journey and ascension, he also saw with certainty in his heart.
It could be that the eye sees something but the heart does not confirm it, and it could be the that heart sees something that the eye does not confirm. As for what the Prophet (sal Allahu alayhi wa sallam) saw during the night of Mi’raaj, it is the truth – in both his sight and in his insight, and that is why Allah ta’ala says: “The heart lied not in what he saw.” (Surah Najm 53:11)

مَا زَاغَ الْبَصَرُ وَمَا طَغَىٰ

“The sight turned not aside, nor it transgressed beyond the limit.” (Surah Najm 53:17)
This ayah is referring to the sight of the Prophet (sal Allahu alayhi wa sallam) during the ascension to the heavens, and the scholars say ”zaagha” means turning to the left and right. As for “wa ma taghaa“; this means he did look past what was in front of him.
The Messenger (sal Allahu alayhi wa sallam) had the best of manners in this high standing; he did not turn his eyes to the left or right, and he did not look to what was not permitted for him to look at and this is from the perfection of the character of the Prophet (sal Allahu alayhi wa sallam).
Normally, you will find people looking around to their right and to their left when they enter a place that is strange to them, especially if this place is a great change from what they are used, such as in this regard (i.e., ascension into the heavens). A person will not be able to keep themselves from looking around to see what is happening but because of the perfection of the Prophet’s (sal Allahu alayhi wa sallam) character, manners, his calmness and self-control, he did not turn aside or transgress the limits.