What is the status of the Hadith:
“One day’s fever expiates a year’s worth of sin.”
This is recorded by Imam Qudha’i (rahimahullah) in his Kitab; Ash-Shihab, hadith: 62 on the authority of Sayyiduna ‘Abdullah Ibn Mas’ud (radiyallahu’anhu) as part of a longer Hadith on fever.
This Hadith is declared sound (hasan) by ‘Allamah Zurqani (rahimahullah)
(Mukhtasar Maqasidul Hasanah, hadith:393 . Also see Maqasidul Hasanah, hadith: 421 & Sharhul ihya, vol.9 pg.526)
Note: Generally Hadiths like the above refer to the expiation of the minor sins. For forgiveness for the major sins, one needs to do sincere tawbah.
And Allah Ta’ala Knows best.