When Negus died, the Messenger of Allah ﷺ informed them of his death and told them to seek forgiveness for him.
حدثنا سفيان عن الزهري عن أبي سلمة
أن رسول الله ﷺ لما مات النجاشي أخبرهم أنه قد مات فاستغفروا له
No references are available.
Its isnad is sahih. Muslim narrated this meaning within a longer hadith, 1:261, from the route of Aqeel and from the route of Salih, both of them from Zuhri from Saeed bin Musayab and Abu Salama from Abu Hurairah. See 7147, and see Muntaqa 1824.