Sunan Ibn Majah
1080
Sahih+3

It was narrated from Anas bin Malik that the Prophet (ﷺ) said:“There is nothing standing between a person and Shirk (polytheism) except leaving the prayer, so if he leaves it he has committed Shirk.”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi