The Prophet ﷺ said, "A prayer in this mosque of mine is better than a thousand prayers in any other mosque, except for the Sacred Mosque."
حدثنا سفيان عن الزهري عن سعيد
عن النبي ﷺ صلاة في مسجدي أفضل من ألف صلاة فيما سواه إلا المسجد الحرام
Its isnad is sahih. Saeed is Ibn Musayab. Muslim narrated the hadith in 1:391, through Sufyan bin Uyayna, with this same isnad, then he narrated it through other routes after it. Bukhari narrated it in 3:54, through Malik, through another route from Abu Hurairah. Qastallani mentioned in 2:283 that Tirmidhi, Nasai, and Ibn Majah also narrated it. Its meaning has already appeared repeatedly from the hadith of Abdullah bin Umar, including numbers 4646 and 6436.