1) First of all, we have verses and hadiths that indicate the Prophet, the Imams and the martyrs are fully alive after they die, and so they can hear our prayers with the power of God. God has granted them such honor.
Second, believers who passes away and are in the Barzakh heaven can hear our prayers too. We have numerous hadiths that when we offer them a good deed, it reaches them, they receive it, and they see the good deed we offered them. So deceased believers can also hear our prayers.
2) A- Sura 3 verse 169
B- Sura 9 verse 105