Musnad Abu Ya'la al-Mawsili 151:45

Abu Bakr narrated to us, Khalid ibn Makhlad narrated to us, Musa ibn Ya'qub al-Zam'i narrated to us, he said: Abdullah ibn Kaysan narrated to me, Abdullah ibn Shaddad ibn al-Had informed me, from his father, from Ibn Mas'ud, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the closest of people to me on the Day of Resurrection are those who send the most blessings upon me."