Dua for the deceased

اَللَّهُمَّ اغْفِرْ لَهُ، وَارْفَعْ دَرَجَتَهُ فِي الْمَهْدِيِّينَ، وَاخْلُفْهُ فِي عَقِبِهِ فِي الْغَابِرِيْنَ، وَاغْفِرْ لَنَا وَلَهُ يَا رَبَّ الْعَالَمِيْنَ، وَافْسَحْ لَهُ فِي قَبْرِهِ، وَنَوِّرْ لَهُ فِيهِ

Transliteration

Alla-humma'gfir lahu (person's name), warfa'a darajatahu fil mahdiyin, wa'khlufhu fi 'aqibihi fil ga-birin, wagfir lana wa lahu ya rabbal' a-lamin, wafsa'ah lahu fi qabrihi, wa nau-wir lahu fihi

Meaning

O Allah, forgive him (person's name), raise his degree among those who are rightly guided, grant him a successor in his descendants who remain. Forgive us and him, O Lord of the Universe, and make his grave spacious, and grant him light in it.

Source: Muslim: 920