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.
There are many narrations proving that the Prophet led other prophets in prayer before ascending to the Heavens on the night of Al-Israa' (Prophetic journey to Jerusalem) and Al-Mi'raaj (the Ascension). This is the opinion of the well-known scholars, such as Al-Qaadhi 'Iyaadh and Ibn Hajar . The second opinion is that the Prophet prayed with them leading them in prayer after descending from the Heavens. This is the opinion of Ibn Katheer and others .
The author of "As-Siraaj" said, "It would be possible that the Prophet prayed with them twice, i.e., before his ascension and after returning.” The prayer performed by the Prophet is the same prayer which is known and performed by all Muslims. This prayer might be a supererogatory prayer or the prayer that was made obligatory before the night of the Ascension.
Imaam An-Nawawi supported the view that this was an obligatory prayer. There are many opinions concerning the matter of prayer, whether there was any obligatory prayer before the night of Al-Israa' or not. Some are of the opinion that before the Ascension of the Prophet there was only a voluntary night prayer which was not compulsory, while some have other opinions.
However, in our opinion this prayer was a non-obligatory one which Prophet Muhammad used to pray before it was made obligatory for him and the entire Ummah (Muslim nation).
Allaah Knows best.