The most detailed narrative of a Norse ship funeral was not written by a Norseman. In 922 the Arab envoy Ahmad ibn Fadlan travelled up the Volga and watched the funeral of a chieftain among the Rus, a people of Scandinavian origin trading on the river, and wrote down what he saw at length: the body held in a temporary grave while grave goods were prepared, the ship drawn up on land, the feasting, the killing of animals, the killing of an enslaved girl who had agreed to accompany her master, and the burning of the ship on shore followed by the raising of a mound.
It is a genuinely valuable text, and it is the only eyewitness description of its kind. It also has to be handled with care on three counts. Ibn Fadlan was an outsider describing a people he found alien, and he says so. He was watching one funeral, of one man, among a diaspora community a long way from Scandinavia. And what he describes matches only part of the archaeology: burning on land is attested, but the wealthy Norwegian burials were not burnt, and the human sacrifice he reports is rare and disputed in the excavated record even where a second body is present in a grave.
Modern scholarship treats the account as evidence for what could happen rather than for what usually did. The atlas records it the same way, and records the killing he describes without either dismissing it as travellers' invention or generalising it into a Norse custom.