Musnad Ahmad 25:1457

Yazid narrated to us, Abbad ibn Mansur informed us, from Ikrimah, from Ibn Abbas, from the Prophet, peace and blessings of Allah be upon him, who said: "The best day for you to be cupped is the seventeenth, the nineteenth, and the twenty-first." And he said: "I did not pass by a company of angels on the night I was taken on the Night Journey, except that they said: 'You must use cupping, O Muhammad.'"