Musnad Ahmad 25:109

Jarir narrated to us, from Qabus, from his father, from Ibn Abbas, who said: "The last hardship the believer encounters is death." And regarding His saying: {On the day the sky will be like molten copper} [Al-Ma'arij: 8], he said: "Like the dregs of oil." And regarding His saying: {In the hours of the night} [Al-Imran: 113], he said: "The middle of the night." And he said: "Do you know what the departure of knowledge is?" He said: "It is the departure of the scholars from the earth."