You will need a powerful reagent to tempt an incubus -- an object that represents great devotion and love. With my scrying, I have located a small figurine that should be suitable for your ritual. Thousands of years ago, the figurine belonged to a young couple. The original owners are no more, but their keepsake has survived to the present day. Follow the road north into Ashenvale, then west and past Maestra's Post. You will see a house nestled amongst the trees. There you will find what you seek.