Musannaf Ibn Abi Shayba 3:6078

Ibn Numayr narrated to us, from Juwaybir, from al-Dahhak, from Abdullah, that it reached him that a group of people were remembering Allah while standing. He came to them and said, "What is this remembrance?" They said, "We heard Allah saying: 'Those who remember Allah while standing, sitting, and on their sides.'" He said, "This only applies if a man is unable to pray standing, so he prays sitting."