Al-Matalib al-'Aliyah 779 — The states of the dying person

It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that he said: "The believer passes away with sweat on the forehead; the fact is that some sins of the believer remain, for which expiation is made at the time of the severity of death so that he becomes pure, and because of this hardship his forehead breaks out in sweat."
Imam Musaddad also reported a similar narration from Yunus through Yazid bin Zuray'.