We know that the first person to enter Paradise is Prophet Muhammad, sallallaahu 'alayhi wa sallam. However, what about the people whom the Prophet, sallallaahu 'alayhi wa sallam, saw in Paradise and Hell when he ascended to the heavens during his 'Israa' (Night Journey) and Mi‘raaj (ascension to Heavens)?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The Prophet never stated in any Hadeeth (narration) that there would be someone who would enter Paradise before he does on the Day of Resurrection. However, the Hadeeths stressing that some people have entered Paradise speak about the migration of souls to the afterworld. For example, in a Hadeeth on the authority of Bilaal when the Prophet heard the sound of his footsteps in Paradise, he asked Bilaal about the deed he had done that admitted him into Paradise before him . [Ibn ‘Asaakir]

According to Al-Haafith Al-‘Iraaqi the Prophet seeing Bilaal in Paradise before him was in his dreams and did not refer to the Day of Resurrection.

In reality, the Prophet will be the first to enter Paradise. There is no contradiction because the case of Bilaal refers to the migration of his soul during his sleep.

 It should be noted that no one knows how this takes place, because it pertains to the Unseen and human senses are unable to perceive it. Therefore, we must believe in it and acknowledge it without trying to understand how. This is because our minds are too limited to comprehend such a matter. This is a true statement from the Prophet in which we must believe. May Allaah The Almighty guide us to what pleases Him.

Allaah Knows best.