Sunan Ibn Majah
2100
Sahih+2

It was narrated from Abdullah bin Buraidah that his father told that :the Messenger of Allah (ﷺ) said: "Whoever says: 'I have nothing to do with Islam,' if he is lying then he is as he said, and if he is telling the truth, his Islam will not be sound

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi