Hadith #3258 (Sunan Abi Dawud)
Book: Oaths and Vows (Kitab Al-Aiman Wa Al-Nudhur)
Narrator(s): Muhammad bin 'Isa bin Hyan محمد بن عيسى بن حيان, Muhammad bin Yahya bin Hiban محمد بن يحيى بن حبان, Yahya bin al-'Ala al-Bijly يحيى بن العلاء البجلي, Yusuf bin 'Abdullah bin Salam
Grade: Sahih

The Prophet (ﷺ) said: If anyone takes an oath and says: I am free from Islam; now if he is a liar (in his oath), he will not return to Islam with soundness.

Source: https://parallelquran.com/hadith/sunan-abi-dawud-3258/