Musannaf Ibn Abi Shayba 2:102

2219. 'Umar ibn Harun narrated to us, from Ibn Jurayj, from 'Ata', he said: I said to him, "Should a man give the adhan while he is sitting?" He said, "No, unless there is an ailment." I said, "Or from drowsiness or laziness?" He said, "No."