All Other Methods Except the Sunnah Are to Be Rejected

Since there is no other prophet to come after the Holy Prophet it is not permitted to adopt any way of life other than his. His ways of life will be prevalent till the day of judgement, admitting no change therein.
Hazrat Jabir has reported it that the Holy Prophet said: "I have brought unto you a white, bright and clean religion. Even if Moses were alive, he would have had no other way but to follow me."

There is another report from Hazrat Jabir that has most probably been cited afore that once Hazrat Umar bin al-Khattab brought a copy of the Torah in the Holy Prophet's presence and said: "O Apostle of Allah! This is a copy of the Torah." At this the Holy Prophet kept silent. So Hazrat Umar began to read it. The Holy Prophet's bright face began to change. At this Hazrat Abu Bakr told Hazrat Umar: “Don't you see the Holy Prophet's luminous face"? So Hazrat Umar looked at his face and said: "I seek Allah's protection from Allah's anger and the Apostle's anger. We sincerely agree with Allah's being our Lord, Islam being our religion, and Muhammad being our prophet."
Then the Holy Prophet said: "By that Being in Whose Possession is my life! Even if Moses comes amongst you and you begin to follow him and leave me, you will go astray from the right path. Were Moses alive and had been contemporary with me he too would have followed me."
This is the reason that with the approach of the Day of judgement when Jesus descends from heaven, he too will follow the Muhammadan Law and the Holy Prophet's way of life.