Is lying to friends about practicing masturbation considered a sin, knowing there is an intention to stop it?

Practicing masturbation is impermissible, and lying is a reprehensible and detested trait in the sight of Allah Almighty. The Prophet, peace and blessings be upon him, said: "Hold fast to truthfulness, for truthfulness leads to righteousness, and righteousness leads to Paradise. A man continues to be truthful and strives for truthfulness until he is recorded with Allah as a siddiq (a truthful one). And beware of lying, for lying leads to wickedness, and wickedness leads to the Fire. A man continues to lie and strives for lying until he is recorded with Allah as a kadhdhab (a great liar)."

You must repent to Allah Almighty from lying and practicing masturbation. Do not admit to committing the sin in front of your friends, for that is a form of publicizing a sin. The Prophet, peace and blessings be upon him, said: "All of my Ummah (nation) will be forgiven except for those who publicize their sins. Indeed, it is a form of publicizing a sin for a man to do something at night, and then in the morning, while Allah has concealed it for him, he says, 'O so-and-so, last night I did such and such.' He had spent the night with his Lord concealing it, but in the morning, he uncovers Allah's concealment from himself."

If you are asked, do not admit to the disobedience and do not lie; rather, use ma'areedh (indirect speech/allusion).