Musannaf Ibn Abi Shayba 3:448

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Abu Khushaynah Hajib ibn ‘Umar, he said: I entered with Al-Hakam ibn al-A’raj upon Bakr al-Muzani while he was ill. He said: "Have you prayed the Asr?" They said: "Yes." So he stood up and prayed a prayer, and he made it light due to his illness.