Hudhaifa reported Allah's Messenger ﷺ as saying: the Dajjal would have with him water and fire and his fire would have the effect of cold water and his water would have the effect of fire, so don't put yourself to ruin. Abu Mas'ud reported: I also heard it from Allah's Messenger ﷺ.
The Prophet Muhammad is reminding us that we should always be aware of false prophets who may try to lead us astray, no matter how convincing they may seem at first glance. He is also warning us against being too trusting or gullible when it comes to matters of faith, as this could lead to disaster for ourselves and those around us if we are not careful enough.