Musnad Abu Ya'la al-Mawsili 110:70

Abu Khaythama narrated to us, Ibn 'Uyaynah narrated to us, 'Amr informed us, from 'Ata', from Ibn 'Abbas, who said: Al-Muhassab is nothing; it is merely a place where the Messenger of Allah (peace and blessings of Allah be upon him) descended.