Musnad Ahmad 788:275

'Abd al-Samad and 'Affan narrated to us, they said: Hammam narrated to us, he said: Abu 'Imran al-Jawni narrated to us that Abu Bakr—and 'Affan said: from Abu Bakr ibn 'Abd Allah ibn Qays al-Ash'ari—informed him, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The tent is a hollowed pearl, its length in the sky is sixty miles. In every corner of it are people for the believer; the others do not see them."