Protect ourselves from this du’a by Rasulallah s.a.w. and Jibril a.s.!
Rasulallah s.a.w. ascended the minbar and said: “Ameen, ameen, ameen.” It was said: ‘O Messenger of Allah, you ascended the minbar and said, ‘Ameen, ameen, ameen.”
He (s.a.w.) said: “Jibril (a.s.) came to me and said: ‘If Ramadhan comes and a person is not forgiven, he will enter Hell and Allah will cast him far away. Say Ameen.’
So I said Ameen…”
(The 2 remaining du’as is made against those whose parents are alive and he does not honour them before he dies, and those who do not send blessings upon Rasulallah s.a.w. whenever his name is mentioned in his presence) 
This du’a is made by the greatest of all the angels, Jibril a.s., and the best of all mankind, Rasulallah s.a.w. AGAINST those who do not take Ramadhan seriously! This is a frightening and heavy du’a made against us mankind, and surely Allah s.w.t. fulfills the du’a of His beloved Messenger s.a.w. if He wills.
We know that Allah s.w.t. has given us so many opportunities, so many incentives for us to gear up in Ramadhan, to earn His Forgiveness. But if we neglect this month, if we don’t take our ibadah seriously, if we refuse to abandon our bad deeds knowingly, we will be one of those who are doomed. May Allah s.w.t. save us.
My brothers and sisters in faith, this is a cry to all of us: Protect ourselves from this du’a. Rejuvenate, get your spirit up! Try to do your best to fully utilize this Ramadhan. And the best way to do that is to treat this Ramadhan as it is your last.
 Narrated by Ibn Hibbaan, 3/188; classed as saheeh by al-Shaykh al-Albaani in Saheeh al-Targheeb, 1679.