“Anyone who learns the language of some people will be safe against their deception.”

Question 16: My question is about the degree of authenticity of the following two transmitted sayings, which are commonly said by people: First: What is ascribed to the Messenger of Allaah (peace be upon him) that he said after returning from one of his battles: “We have returned from the lesser Jihaad (striving in the Cause of Allaah) to the greater Jihaad (the inward spiritual struggle).” Second: What is also ascribed to him that he (peace be upon him) said: “Whoever learns the language of some people will be safe against their deception.”

Answer: As for the first Hadeeth reporting that the Messenger of Allaah (peace be upon him) said after returning from one of his battles… read more here.