Musannaf Ibn Abi Shayba 27:149

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