Although it was Rameses III who built the Great Temple for Khonsu in Thebes it seems that this legend was recorded some time after.
Pharaoh was in the country of Nehern (thought to be in Western Syria near the Euphrates river), collecting his annual tribute, when the Prince of Bekhten came with the other chiefs to salute him and to present gifts. The other chiefs brought gold, lapis-lazuli, turquoise, and precious woods, but the Prince of Bekhten also offered his eldest daughter (who was very beautiful) as a wife. Pharaoh accepted, and took her back to Egypt, where he made her the chief royal wife and named her Ra-neferu (“the beauties of Ra”).
Some time later, during the fifteenth regnal year, the Prince of Bekhten visited Thebes and presented offerings to the king and paid homage to him. He explained that Queen Ra-neferu’s younger sister Bent-Reshet (or Bent-enth-reshet) was very ill and he implored Pharaoh to send one of his physicians. The king immediately summoned all of the learned men of his court and asked them to choose a skilled physician to travel to Bekhten and heal the Queen”s young sister. They chose the royal scribe Tehuti-em-beb and he set off to see the poor girl. When he examined her he realised that her illness was the work of an evil spirit, which could not exorcise. So the Prince of Bekhten asked Pharaoh to send a God to combat the spirit.
The envoy arrived in Egypt during the festival of Amun. When the Pharaoh heard the message he went straight to the temple of Khonsu Nefer-hetep, and said to the god, “0 my fair Lord, I have come once again into thy presence to petition you on behalf of the daughter of the Prince of Bekhten.” The God imbued a statue of him with power and this image was sent to Beketen. After a journey of seventeen months. The god confronted the demon, who left the girl immediately, and she was cured. Then the demon spoke to Khonsu, recognising his power and asking for forgiveness. However, he also asked that a feast be held for himself and Khonsu before he left the mortal world for his own lands. A great fest was held and everyone had a great time, then the demon went home as promised.
The Prince realised how powerful Khonsu was and decided to keep his image in Bekhten. But after three years, Khonsu decided to return to Egypt in the form of a golden hawk. When the Prince saw this he felt ashamed for trying to keep the god there, and sent back all of the belongings of the god together with numerous offerings and gifts. When the tribute arrived in Egypt the pharaoh placed it at the foot of the statue of Khonsu in the Great Temple.
Adapted from “The Gods of the Egyptians” E.A. Wallis Budge