I would like to know about Mi'raj, with specific emphasis on the issue of whether the Mi'raj was physical or spiritual.

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The majority of the Muslim scholars agree that the Israa' and Mi'raaj were both physical and spiritual. Although some scholars say that only the spirit of the Prophet ascended, the most sound opinion is the first one. Ibn Jareer said, 'It is meaningless to say that only the Rooh (spirit) of the Prophet ascended during the Israa' and Mi'raaj as if this is the case, this phenomenon would not be considered as an evidence to the Prophet's prophecy nor would it be considered a proof for the revelation nor would those who deny it be considered apostates'.

And the verse (which means): {"Glorified (and Exalted) be He (Allaah) [above all that (evil) they associate with Him] Who took His slave (Muhammad (sallallaahu ‘alayhi wa sallam) for a journey ……."}[Quran 17:1] also does not denote that taking him for a journey by night means taking his soul only. Moreover, the authentic narrations prove the fact that Al-Buraq (a riding animal from Heaven) was brought to him and he went on his sacred journey riding on this animal. If the Mi'raaj were with his soul only, the soul would not ride on Al-Buraq. Imaam Ibn Katheer said, 'If the Israa' were in sleep no doubt it would not astonish the People of Makkah and they would not accuse him of lying, and some of the new Muslims would not become apostates'. A person consists of a body and a soul. Allaah The Almighty Says (what means): {The sight (of Prophet Muhammad (sallallaahu Alayhi wa sallam) turned not aside (right or left), nor it transgressed beyond the limit (ordained for it).}[Quran, 53:17] Sight is a part of body, not the soul. For more details you may refer to Tafseer of Ibn Katheer and other Tafseer books concerning this subject.

Allaah Knows best.