"And from among his (shaytaan’s) repertoire of schemes and ploys is that he invites the slave (of Allaah) with his good character, cheerfulness and joyfulness to types of sin and wickedness. As a result, he will meet and greet him (the sunnee) with that which will not enable him to rescue himself from his evil except his display of displeasure, giving an angry look and turning away from him. So, the enemy will act kindly towards him, greeting him with joyfulness, a glowing face and beautiful speech. Then, he will attach himself to him, and have a strong desire to save himself from his clutches, however he will be unable to. As a result, the enemy (Iblees) will continue to move among them (the deviant, innovator that works for Shaytaan and against the sunnee slave) until he achieves his desired goal. Finally, he enters upon the slave with his plots by way of good character and a shining face. It is for this reason, the 'Doctors of the Heart' have advised (us) with turning away from the People of Innovation, not extending to them the greetings of salaams and happy, glowing faces or even meeting them (at all) unless it is with gloominess and sternness!"
Taken from Ighaathatul Lahfaan 1/140