Short answer
Isra ("night journey") is the Prophet's ﷺ journey by night from Makkah to Jerusalem. Mi'raj ("ascent") is his ascent from Jerusalem through the seven heavens, where the five daily prayers were given. Both happened on the same night, before the Hijrah.
The majority of Sunni scholars hold that the Isra is established by the Quran (17:1) and the Mi'raj by sound, widely narrated hadith, with Surah al-Najm (53:13-18) referring to it, and that both happened in one night, in body and soul, while he was awake.
The four schools agree on this.
Explanation
Isra comes from an Arabic root meaning to travel by night. In the seerah it means the journey of the Prophet ﷺ from al-Masjid al-Haram in Makkah to al-Masjid al-Aqsa in Jerusalem, on the Buraq, a white animal smaller than a mule and larger than a donkey, whose stride reached as far as its sight. In Jerusalem he led the prophets in prayer. Surah al-Isra (17) opens with this journey.
Mi'raj means a ladder or means of ascent. From Jerusalem he rose with Jibril through the seven heavens, meeting prophets such as Adam, Isa, Yahya, Yusuf, Idris, Harun, Musa and Ibrahim. He reached the Lote Tree of the Utmost Boundary (Sidrat al-Muntaha), saw great signs of his Lord, and was given the prayers, reduced from fifty to five with the reward of fifty. Surah al-Najm alludes to this.
The year is debated. Many scholars place it about a year to a year and a half before the Hijrah, after the deaths of Khadijah and Abu Talib. The date often marked, 27 Rajab, is a popular view, but scholars give other dates too. Most scholars hold that it happened in body and soul, awake, which is why Quraysh mocked it and why Abu Bakr's immediate belief earned him the name al-Siddiq.
For the full story and the dates for this year, read Isra and Miraj. For Jerusalem's place in it, see Why is Jerusalem important in Islam?
The evidence
Quran, Surah Al-Israa 17:1
بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ سُبْحَٰنَ ٱلَّذِىٓ أَسْرَىٰ بِعَبْدِهِۦ لَيْلًۭا مِّنَ ٱلْمَسْجِدِ ٱلْحَرَامِ إِلَى ٱلْمَسْجِدِ ٱلْأَقْصَا ٱلَّذِى بَٰرَكْنَا حَوْلَهُۥ لِنُرِيَهُۥ مِنْ ءَايَٰتِنَآ ۚ إِنَّهُۥ هُوَ ٱلسَّمِيعُ ٱلْبَصِيرُ ﴿١﴾
Exalted is He who took His Servant by night from al-Masjid al-Haram to al-Masjid al-Aqsa, whose surroundings We have blessed, to show him of Our signs. Indeed, He is the Hearing, the Seeing.
The Isra.
Quran, Surah An-Najm 53:13-14
وَلَقَدْ رَءَاهُ نَزْلَةً أُخْرَىٰ ﴿١٣﴾ عِندَ سِدْرَةِ ٱلْمُنتَهَىٰ ﴿١٤﴾
And he certainly saw him in another descent At the Lote Tree of the Utmost Boundary -
The Mi'raj and the Lote Tree.
Quran, Surah An-Najm 53:18
لَقَدْ رَأَىٰ مِنْ ءَايَٰتِ رَبِّهِ ٱلْكُبْرَىٰٓ ﴿١٨﴾
He certainly saw of the greatest signs of his Lord.
He saw great signs on that night.
Sahih Muslim 162
Sahih... أتيت بالبراق وهو دابة أبيض طويل فوق الحمار ودون البغل ...
"The Buraq was brought to me: a tall white animal, larger than a donkey and smaller than a mule."
The start of his account of the Isra and Mi'raj.
Where the ruling is recorded
- Fath al-Bari (Ibn Hajar), Commentary on Kitab Manaqib al-Ansar, chapter on the Mi'raj. Discusses the date and whether it was in body and soul.
- Zad al-Ma'ad (Ibn al-Qayyim), Section on the Isra and Mi'raj. Ibn al-Qayyim's summary of the events and the debate on dates.
- al-Bidaya wa al-Nihaya (Ibn Kathir), Chapter on the Isra and Mi'raj. Gathers the hadith of the night.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.