The Prophet (ﷺ) used to say in funeral prayer:
اَللَّهُمَّ اغْفِرْ لِحَيِّنَا وَمَيِّتِنَا وَصَغِيرِنَا وَكَبِيرِنَا وَذَكَرِنَا وَأُنْثَانَا وَشَاهِدِنَا وَغَائِبِنَا اَللَّهُمَّ مَنْ أَحْيَيْتَهُ مِنَّا فَأَحْيِهِ عَلَى الْإِيمَانِ وَمَنْ تَوَفَّيْتَهُ مِنَّا فَتَوَفَّهُ عَلَى الْإِسْلَامِ اَللَّهُمَّ لَا تَحْرِمْنَا أَجْرَهُ وَلَا تُضِلَّنَا بَعْدَهُ
اَللّٰهُمَّ اغْفِرْ لِحَيِّنَا وَمَيِّتِنَا وَصَغِيْرِنَا وَكَبِيْرِنَا وَذَكَرِنَا وَاُنْثَانَا وَشَاهِدِنَا وَغَائِبِنَا اَللّٰهُمَّ مَنْ اَحْيَيْتَهُ مِنَّا فَاَحْيِهٖ عَلَى الْاِيْمَانِ وَمَنْ تَوَفَّيْتَهُ مِنَّا فَتَوَفَّهٗ عَلَى الْاِسْلَامِ اَللّٰهُمَّ لَا تَحْرِمْنَا اَجْرَهٗ وَلَا تُضِلَّنَا بَعْدَهٗ
Allahum-maghfir lihayyinaa, wa mayyitinaa, wa sagheerinaa wa kabeerinaa, wa thakarinaa wa 'unthaanaa, wa shaahidinaa, wa ghaa'ibinaa. Allaahumma man 'ahyaytahu minnaa fa'ahyihi 'alal-'Imaan, wa man tawaffaytahu minnaa fatawaffahu 'alal-'Islam, Allaahumma laa tahrimnaa 'ajrahu wa laa tudhillanaa ba'dahu
O Allah, forgive those of us who are living and those of us who are dead, those of us who are present and those of us who are absent, our young and our old, our male and our female. O Allah, to whomsoever of us You givest life grant him life as a believer, and whomsoever of us You takest in death take him in death as a follower of Islam. O Allah, do not withhold from us the reward (of faith) and do not lead us astray after his death.