- on ashabul kahf (the people of the cave)
- on ruh and
- on the man who went around the globe i.e. Dhul-Qarnain.
For two of the questions, Allah guided the Prophet to answer them as recorded in Surah Kahf. And the other question was answered in another verse. There are 16 places in the Qur'an where Prophet Muhammad was questioned - "Yas alu naka anil..." and Allah inspired him to answer by saying Qul, "Say O Muhammad.." Out of the 16 questions directed to the Prophet, one question was answered directly by Allah. It was a question pertaining to ruh (spirit). "When they ask you about me, say I am near". The Qur'an says "fa inni qarib" and not "qul inni qarib". Notice that the question was about Allah Ta'ala so He the Exalted is He was the one who answered directly. Furthermore, the ayah is related to du'a. Prophet Muhammad was also asked on whether Allah was far that we have to shout to Him or if He was near that we should only whisper our petitions. Know that the ayah actually mentioned the word qabul first before du'a. What it means is that Allah grant your wish even before you begin to ask. The door for du'a is already opened even before you knock on its door! One who does not make du'a is mutakabbir (proud). By contrast one who is muttar is one who only focuses on Allah as his only savior, so his du'a is directed to Allah wholeheartedly because he is desperate for His help. Allah will immediately answer the du'a of one who is muttar. His du'a is qabul instantaneously.