Musnad Ahmad 25:589

Surayj ibn al-Nu‘man narrated to us, Hushaym narrated to us, from Abu Bishr, from Sa‘id ibn Jubayr, from Ibn ‘Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The report is not like the witnessing. Indeed, Allah (Mighty and Majestic is He) informed Musa of what his people had done regarding the calf, yet he did not cast down the tablets. But when he witnessed what they had done, he cast down the tablets and they broke."