The Messenger of Allah ﷺ said, "Whoever revives a sunnah of mine and people act upon it will have a reward equal to that of everyone who acts upon it, without diminishing their rewards in the least. And whoever introduces an innovation and people act upon it will bear the sins of all who act upon it, without diminishing their sins in the least."
حدثنا أبو بكر بن أبي شيبة حدثنا زيد بن الحباب
أن رسول الله ﷺ قال من أحيا سنة من سنتي فعمل بها الناس كان له مثل أجر من عمل بها لا ينقص من أجورهم شيئا ومن ابتدع بدعة فعمل بها كان عليه أوزار من عمل بها لا ينقص من أوزار من عمل بها شيئا
[Its chain is very daif] Reported by Tirmidhi, chapter on knowledge, "The section on adhering to the sunnah," no. 165 (regarding its condition, and avoiding innovation), no. 2677, from the hadith of Kathir with this wording, and he said, hasan. Kathir has been mentioned before.