Is the hadith about the Prophet eating dates with butter authentic, and is eating buttered dates a Sunnah of the Prophet?

Summary

The hadith narrated by Abu Daud about the Prophet liking butter and dried dates has a chain of narration judged authentic by Sheikh Shu‘aib al-Arna’ut. The food and eating habits of the Prophet fall under the broad category of non-legislative Sunnah, so the emphasis is on the purpose and wisdom behind them, such as eating healthy food, avoiding excess and waste. The butter of the Prophet's time may have differed somewhat from that sold today. Whoever eats dates and butter intending to follow the Prophet is rewarded because of love for him.

Written in our own words from the original fatwa — check the source before acting on it.