Musannaf Ibn Abi Shayba 33:1103

'Affan ibn Muslim narrated to us, he said: Salam ibn Miskin narrated to us, he said: 'Imran ibn 'Abd Allah ibn Talha al-Khuza'i narrated to us, he said: The soul of Sa'id ibn al-Musayyib was lighter to him, for the sake of Allah, than the soul of a fly.