Musnad Ahmad 1185:2

Ibrahim and Yunus narrated to us, they said: Abd al-Rahman narrated to us, he said: And my father narrated to me, from his mother, Aisha bint Qudamah, she said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "It is dear [difficult/unlikely] to Allah, the Almighty and Majestic, that He should take the two precious things of a Muslim, then enter him into the Fire." Yunus said: "Meaning: his two eyes."