Abu Zaid Thabit bin Ad-Dahhak Al-Ansari (May Allah be pleased with him( (he is one of those who gave their pledge of allegiance to the Messenger of Allah ﷺ under the Tree) said:
The Messenger of Allah ﷺ said, "He who swears by a religion other than that of Islam, is like what he has professed. He who kills himself with something, will be tormented with it on the Day of Resurrection. A person is not bound to fulfill a vow about something which he does not possess. Cursing a believer is like murdering him."

[Al-Bukhari and Muslim].

عن أبي زيد ثابت بن الضحاك الأنصاري رضي الله عنه، وهو من أهل بيعة الرضوان قال: قال رسول الله ﷺ : "من حلف على يمين بملة غير الإسلام كاذبًا متعمدًا، فهو كما قال، ومن قتل نفسه بشيء، عُذب به يوم القيامة، وليس على رجل نذر فيما لا يملكه، ولعن المؤمن كقتله" ((متفق عليه)).