The Children of Israel worshipped the Calf

Sahih International[Ayah 2:51]

 

And [recall] when We made an appointment with Moses for forty nights. Then you took [for worship] the calf after him, while you were wrongdoers.

Sahih International[Ayah 2:52]

 

Then We forgave you after that so perhaps you would be grateful.

Sahih International[Ayah 2:53]

And [recall] when We gave Moses the Scripture and criterion that perhaps you would be guided.

Allah then said, "Remember My favor on you when I forgave you for worshipping the calf.'' This happened after Musa went to the meeting place with his Lord at the end of that period which was forty days.

These forty days were mentioned in Surat Al-A`raf, when Allah said,

(And We appointed for Musa thirty nights and added (to the period) ten (more)) (7:142).

It was said that these days were during the month of Dhul-Qa`dah plus the first ten days in Dhul-Hijjah, after the Children of Israel were delivered from Fir`awn and they safely crossed the sea. Allah's statement,

 (And (remember) when We gave Musa the Scripture) means, the Tawrah,(And the criterion) that is that which differentiates between truth and falsehood, guidance and deviation.

(So that you may be guided aright), after escaping the sea, as another Ayah in Surat Al-A`raf clearly stated,

 (And indeed We gave Musa ـ after We had destroyed the generations of old ـ the Scripture (the Tawrah) as an enlightenment for mankind, and a guidance and a mercy, that they might remember (or receive admonition)) (28:43).