Is it permissible for me to say, "I dreamt," when I did not, for the sake of a benefit?

Lying is forbidden (haram), but lying about a dream is even more forbidden and carries a greater punishment. This is due to the Prophet's (peace be upon him) saying: "Whoever claims to have seen a dream which he has not seen will be ordered to tie two barley grains together." This is also because a true dream is a part of prophecy, and one who lies about his dream claims that Allah Almighty showed him what He did not. Lying about Allah is a greater fabrication than lying about creation or oneself.