Verily the Messenger of Allah ﷺ said: He who took an oath on a religion other than Islam as a liar would become so as he said, and he who slaughtered himself with a thing would be slaughtered with that on the Day of Resurrection. (Using translation from Muslim 110d)
قَالَ رَسُولُ اللهِ ﷺ مَنْ حَلَفَ بِمِلَّةٍ سِوَى الْإِسْلَامِ كَاذِبًا مُتَعَمِّدًا فَهُوَ كَمَا قَالَ وَقَالَ مَنْ قَتَلَ نَفْسَهُ بِشَيْءٍ عَذَّبَهُ اللهُ بِهِ فِي نَارِ جَهَنَّمَ