Imam Ahmad recorded in his Musnad, that a person who was riding behind the Prophet said, “We were on a trip when the Prophet’s animal tripped, so I said, `Cursed is Shaytan.’ The Prophet (sallAllahu ‘Alyhi wasallam) heard this & said •► “Do not say, ‘Cursed is Shaytan,’ for if you say these words, Shaytan becomes arrogant & stronger and says, ‘With my strength I made him fall.’ Instead say, ‘Bismillah,’ for if you say that Shaytan will become as small & weak as a fly.”
[An-Nasai 6/142, Ahmad 5/59 & Abu Dawud 4946]