It is narrated from Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) informed the people of the death of Najashi on the very day he passed away. Then he went with the people to the place of prayer, led them in congregational prayer, and said four takbirs in the (funeral) prayer.
Hadith Referenceمسند الإمام الشافعي / كتاب الجنائز / 597
Hadith Takhrijاخرجه البخاري، الجنائز، باب الرجل ينعى إلى اهل الميت بنفسه (1245) ۔ ومسلم، الجنائز، باب في التكبير على الجنازة (951)۔