The Messenger of Allah ﷺ used to fast until we would say he never broke his fast, and he would go without fasting until we would say he never fasted.
حدثنا محمد بن عبيد حدثنا عثمان بن حكيم قال سألت سعيد بن جبير عن صوم رجب كيف ترى فيه قال
أن رسول الله ﷺ كان يصوم حتى نقول لا يفطر ويفطر حتى نقول لا يصوم
Its isnad is sahih, and it is a repetition of no. 2046 with this same isnad. It carries the same meaning as no. 2949.