Musannaf Ibn Abi Shayba 33:549

Jarir narrated to us, from Mansur, from Sa’id ibn Jubayr, from Ibn Abbas regarding His saying: "The whisperer, the slinking one" (al-waswas al-khannas). He said: "Satan is perched upon the heart of the son of Adam. So when he is heedless and negligent, he whispers. And when he remembers Allah, he slinks away."