I said, "After that, I heard a sound that really frightened me. When I asked as to what it was, the reply came: `That sound was from a rock which had been thrown into the fire of hell seventy years ago, that just now landed in its spot and just settled.'"
It has been said that from that time on, the Prophet was never seen to laugh as long as he was alive.
"We continued our trip upwards until we reached the upper atmosphere of the world. There, I saw an angel named Isma'il. He was the custodian of Khitfah which the Qur'an explains as follows:
"Some of them who covertly steal words from the heavens are pursued by a glistening flame. " 
"Under the supervision of Isma'il was seventy thousand angels and under the supervision of each of these (seventy thousand) angels were another seventy thousand angels. He (Isma'il) asked Jibra'il, "Who is this person with you?" The answer was given that: "He is Muhammad" who has been raised up with The Message."
"That Angel opened the door and we entered into the heavens. I greeted him and prayed for his forgiveness. He too greeted me and prayed for my mercy. He said, `Welcome O' Brother and O' Great Prophet.' At that time a group of Angels greeted me. All of them were smiling and were cheerful; except for one of them who had a very hideous appearance (whose name is Khazin), who was upset and crying. No sign of happiness could be seen on his face.
"We were all awed by this Angel. Jibra'il said, `This Angel is the igniter of the fire of Hell. From the time that Allah appointed him as the one who would ignite the fire of hell up until now, he has never smiled. Every day, his anger on the enemies of Allah and those who commit sins increases. It is through this Angel that Allah will punish the sinners. If it was decreed that there should be a smile on his face, then because of you it would have been, but never has he smiled, nor will he ever ‑ neither before you nor after you.' I greeted him and he replied my greeting and he gave me the glad tidings of paradise.
Khazin asked, `Do you give me permission to show (you) the fire of Hell?' Jibra'il replied, `Yes, show the Prophet the fire of hell.' Khazin lifted up the cover of the hellfire and opened the door. Flames from the fire shot up into the sky ‑ flames that were boiling and continuously shooting up. I thought that soon the flames would come close to me. I said, `Jibra'il, tell the Angel to cover up the fire.' He gave the command and the fire went back to its place and Khazin closed the doors of hell and fire."
From Bihar al-Anwar, Vol. 18, p. 320-321, Bab 3 - Ithbaat al-Mi`raaj wa ma`anaahu wa kayfiyyatuhu wa sifatuhu wa ma jaraa feehi wa wasf al-buraaq, Hadith 34.
 Surah Saffat (37), Verse 10