Generally, to tell a lie is considered to be a sin. But if you tell a lie with a bonafide, benevolent, humanitarian, unselfish, pious motive for the good of the society at large
it is not binding in the cycle of birth and death.

Taking an example from Mahabharata, King Yudhisthira who had earned a reputation as a dedicated champion of truth and was famous for his truthfulness had never told
a lie during his whole lifetime. But only once, during the Mahabharata war, a critical situation arose in which Lord Krishna himself compelled him to make an ambiguous
announcement against his will: 'Ashvatthama is killed in the battle.' In fact, an elephant named Ashvatthama was killed and not the son of Guru Dronacharya whose name was also Ashvatthama. But on hearing this announcement from the mouth of such a most famous truthful person, Yudhishthira who had a spotless reputation as a synonym for Truth, Guru Dronacharya took it to be the gospel truth that his own son was killed and he immediately left the battle field which made it very easy for Yudhishthira to win the war. If Yudhishthira would not have made such an ambiguous,
misguiding and totally false statement, there were no hopes for him to win the war and defeat the rascal kings who were horribly dangerous to the society and the country. This action (Kriyaman Karma) of telling a lie on the part of Yudhishthira and the abetment thereof on the part of Lord Krishna was not considered as a sin because it was done with the most bonafide and humanitarian, benevolent and pious intention to get rid of the rascals from the earth.