Allah Taala said in Quran:
[Shakir 4:57] And (as for) those who believe and do good deeds, We will make them enter gardens beneath which rivers flow, to abide in them for ever; they shall have therein pure mates, and We shall make them enter a dense shade.
[Shakir 4:122] And (as for) those who believe and do good, We will make them enter into gardens beneath which rivers flow, to abide therein for ever; (it is) a promise of Allah, true (indeed), and who is truer of word than Allah?
[Shakir 29:9] And (as for) those who believe and do good, We will most surely cause them to enter among the good.
So moslems from all world believe that Allah is the One and only who could make someone enter heaven or hell.
Let us see what shias say.
Abu Abdullaah said : ‘When it is the Day of Judgement, a pulpit will be put in place of which all the creation will see it : and a man will stand on it and on his right hand there is an angel and on his left hand there is angel standing with him.
Then the one on his right hand will announce : ‘ O congregation of creatures this is Alee ibn Abee Taalib the owner of paradise : he enters into it whoever he wills.
Then the one on his left hand will announce : ‘ O congregation of creatures this is Alee ibn Abee Taalib the owner of hell fire : he enters into it whoever he wills.’
Ayatullat Dastghaib Shirazi
“Moral values of Quran”
Chapter “Ali with his own bier” (p 257)
Harith Hamadani had become very old, bent at the waist and ill. He reached Ali with much difficulty and said how much I desired to look at your beautiful face, O Master! I have come to you from a long distance, as I was deprived of this honor due to my old age and weakness. Ali told him, “O Harith! Everyone who dies sees me. I tell you that you will also see me near Sirat bridge (in the Hereafter). I will be there do distribute Paradise and hell to people. I place the righteous in Paradise and the evil people in hell. If any of my friend is in hell, I fetch him out from the fire.”