Jannah is located close to the Sidrat-ul-Muntaha. In the Qur’aan Majeed, Allah Ta‘ala says:
عِنۡدَ سِدۡرَۃِ الۡمُنۡتَہٰی ﴿۱۴﴾ عِنۡدَہَا جَنَّۃُ الۡمَاۡوٰی ﴿ؕ۱۵﴾
At Sidrat-ul-Muntaha, near it is Jannat-ul-Ma’waa (the abode of Jannah). (Surah Najm v. 14-15)
It is reported in the narration of Hazrat Abu Sa’eed Khudri (radhiyallahu ‘anhu) that after performing salaah in Bayt-ul-Ma’moor, Rasulullah (sallallahu ‘alaihi wasallam) was raised to the Sidrat-ul-Muntaha. Thereafter, Rasulullah (sallallahu ‘alaihi wasallam) was raised to Jannah, and after his visit to Jannah, Jahannum was presented before him. In other words, the horrors of Jahannum were laid bare before him.
In another narration, Hazrat Abu Zar (radhiyallahu ‘anhu) reports that Rasulullah (sallallahu ‘alaihi wasallam) said, “I reached Sidrat-ul-Muntaha where I beheld amazing and wonderful colors and sights. I do not know what they were. Thereafter, I was admitted into Jannah where I had seen that the domes were constructed from huge pearls and the soil was of musk.”
(Extracted from Seeratul Mustafa 1/303-304)