Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: "Indeed, Allah Almighty looked at the hearts of His servants and found the heart of Sayyiduna Muhammad (peace and blessings be upon him) to be the best of all hearts, so He chose him for Himself and sent him (peace and blessings be upon him) with His message."
This narration has already passed in full before this in the chapter on consensus (ijma').
Ahmad, al-Bazzar and al-Tabarani recorded it in al-Mu'jam al-Kabir and al-Mu'jam al-Awsat, and its narrators have been declared trustworthy.