Jami` at-Tirmidhi, Volume 2, Book 8, Hadith 1025 (DarusSalam) ⓘ
Awf bin Malik said: "I heard the Messenger of Allah, while he was performing Salat for a deceased person. I could hear him saying in his prayer: (Allahummagfir lahu, war hamhu, waghsilhu bil-baradi (waghsilhu) kama yughsaluth-thawb) 'O Allah! Forgive him, have mercy upon him, and wash him with (snow or ice) (and wash him) just as a garment is washed.'"
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا مُعَاوِيَةُ بْنُ صَالِحٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ جُبَيْرِ بْنِ نُفَيْرٍ، عَنْ أَبِيهِ، عَنْ عَوْفِ بْنِ مَالِكٍ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُصَلِّي عَلَى مَيِّتٍ فَفَهِمْتُ مِنْ صَلاَتِهِ عَلَيْهِ " اللَّهُمَّ اغْفِرْ لَهُ وَارْحَمْهُ وَاغْسِلْهُ بِالْبَرَدِ وَاغْسِلْهُ كَمَا يُغْسَلُ الثَّوْبُ " . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ . قَالَ مُحَمَّدُ بْنُ إِسْمَاعِيلَ أَصَحُّ شَيْءٍ فِي هَذَا الْبَابِ هَذَا الْحَدِيثُ .
also referenced under: Hadith 1025 (Reference) & Book 10, Hadith 61 (In-Book)