This excerpt is taken from Sheikh Abu Hamza Abdul Khaliq Siddiqi's book Sahih Fazail-e-Amaal.
The Holy Quran has informed that the habit of the believers is that when they raise their hands in supplication before their Lord, they also pray for all their past Muslim brothers:
﴿رَبَّنَا اغْفِرْ لَنَا وَلِإِخْوَانِنَا الَّذِينَ سَبَقُونَا بِالْإِيمَانِ وَلَا تَجْعَلْ فِي قُلُوبِنَا غِلًّا لِّلَّذِينَ آمَنُوا رَبَّنَا إِنَّكَ رَءُوفٌ رَّحِيمٌ﴾
"O our Lord! Forgive us as well as our brothers who preceded us in faith. And do not place in our hearts any hatred towards the believers. Our Lord! Indeed, You are Most Kind and Most Merciful."
Reference: (59-Al-Hashr:10)