Why Prophet Muhammad Sws Doubted It When All The Prophets Are Guaranteed Jannah?
This is a principle statement that no one actually can fulfill the criteria to enter the paradise, as it is the abode of eternal blessings and we cannot do eternal good to earn it, nor can we abstain completely from mistakes and sins. The prophets on the other hand had been assured by God that they did earn the favour of God. Having said that, God will judge us according to our capacity, that is why the criterion is lowered and this is justice.