Musnad Ahmad 32:879

'Abd al-Malik and 'Abd al-Samad narrated to us, they said: Hisham and 'Abd al-Wahhab narrated to us, he said: Hisham informed us, from Qatadah, from Anas ibn Malik, that the Prophet, peace and blessings of Allah be upon him, said: "There is no contagion, and no evil omen, but the *fa'l* (optimistic word) pleases me." It was said: O Prophet of Allah, what is the *fa'l*? He said: "The good word." Abu 'Amir said: Or he said: "The righteous word."