Prophet (peace be upon him) said Ameen thrice when Jibreel come and said..

Kaab Ibn Ujrah (RA) relates that Rasulullah (peace be upon him) said Come near to the mimbar and we came near the mimbar. When He (peace be upon him) climbed the first step of the mimbar, He (peace be upon him) said “Aameen”, When He (peace be upon him) ascended the second step, He (peace be upon him) said “Aameen”, When He (peace be upon him) climbed the third step, He (peace be upon him) said “Aameen” When He (peace be upon him) came down, We said “O Rasool of Allah (peace be upon him), we have heard from you today something which we never heard before” He (peace be upon him) said When I climbed the first step, the angel Jibraeel (alaihi as-salam) appeared before me and said

“Destruction to him who found the blessed month of Ramdhan and let it pass by without gaining forgiveness”

upon that I said ‘Aameen’. When I climbed the second step, he said,

“Destruction to him before whom thy name is taken and then he does not make Dua for Allah’s blessing on me (by saying, for example , Sallallaahu alaihi wa sallam).”

I replied ‘Aameen’. When I climbed the third step, he said

“Destruction unto him in whose lifetime his parents or either one of them reaches old age, and (through failure to serve them) he is not allowed to enter Jannah”.

I said ‘Aameen’. (Hakim, Baihaqi)

Note In this Hadith, it appears that Jibraeel (alaihi as-salam) gave expression to three curses, upon which Rasulullah (peace be upon him) said Aameen every time. In al-Durr al-Mansoor it is reported that Jibraeel (alaihi as-salam) advised Rasulullah (peace be upon him) to say Aameen. Being an angel of such high mark, Jibraeel ‘s giving these curses is sure to be accepted. May Allah (Subhanahu wa Taala) in His infinite mercy grant us His help and save us from these three dangers.