How are Sunnah and disliking established, and is a special proof required for every Sunnah or disliked act? What is the decisive word on using analogy (qiyas) in acts of worship, especially in chapters of purification, prayer, and fasting?

The Sunnah (definition) is the absolute path. The Messenger of Allah, peace and blessings be upon him, said: "Whoever introduces a good practice (sunnah hasanah) in Islam and it is acted upon after him, will have the reward of whoever acts upon it."