Surah Ali 'Imran 3:24

ذَٰلِكَ بِأَنَّهُمْ قَالُوا۟ لَن تَمَسَّنَا ٱلنَّارُ إِلَّآ أَيَّامًا مَّعْدُودَٰتٍ ۖ وَغَرَّهُمْ فِى دِينِهِم مَّا كَانُوا۟ يَفْتَرُونَ

That is because they say, "Never will the Fire touch us except for [a few] numbered days," and [because] they were deluded in their religion by what they were inventing.

Translation: Saheeh International

Tafsir

That turning away and rejection was because they said ‘the Fire shall not touch us except for a number of days’ that is for forty days only the length of time their forefathers worshipped the calf after which it would end; …

Excerpt from Tafsir al-Jalalayn, commentary on 3:24, via Quran.com. The reader has the full commentary and 9 more tafsirs.