Is it a sin(of suicide) to sacrificing your own life to save other person, in a situation where you know that you will die if you save the other person. Will this act count as suicide or will you get reward in the hereafter?
Bismillah. Alhamdulillahi rabbil-'alamin. Was-Salatu was-Salam 'ala Ashraful Anbiya Sayyidina Muhammad wa 'ala 'Alihi Muhammad.
Saving a life at the cost of sacrificing own is a sign of bravery, courage and valor. Allah deeply loves such people and will reward them in such abundance that one cannot imagine. In following verse Allah speaks about this.
Because of that, We decreed upon the Children of Israel that whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely. And whoever saves one - it is as if he had saved mankind entirely. And Our messengers had certainly come to them with clear proofs. Then indeed many of them, [even] after that, throughout the land, were transgressors.
Pay attention how Allah is stressing greatness of this deed - saving an innocent life. It is equal to saving mankind entirely.