ENOfficial
Abu Hurairah (RAA) narrated that the Messenger of Allah (ﷺ) said, “If you offer the funeral prayer for a deceased person, supplicate Allah sincerely for him." Related by Abu Dawud.
Source: sunnah.com
Other translations
Arabic
وَعَنْهُ أَنَّ اَلنَّبِيَّ - صلى الله عليه وسلم -قَالَ: { إِذَا صَلَّيْتُمْ عَلَى اَلْمَيِّتِ فَأَخْلِصُوا لَهُ اَلدُّعَاءَ } رَوَاهُ أَبُو دَاوُدَ, وَصَحَّحَهُ ابْنُ حِبَّانَ 1 .
sunnah.com