The prohibition against committing suicide:[1]

It is forbidden to commit suicide and one who does so is guilty of murder, as the verse^[2] states “Veach Es Dimchem Lenafshoseichem Edrosh.” [From this verse we learn that one who kills himself, G-d will demand his soul from his hand in the future.^[3] Some write that one who commits suicide does not have a portion in the world to come.^[4] All forms of suicide are prohibited even if blood is not spilled, such as through strangulation.^[5] Some Poskim^[6] learn that one to commit suicide transgresses the prohibition of murder. However, other Poskim^[7] rule that suicide is not included within the murder prohibition and it is its own separate prohibition. Some Poskim^[8] rule that the prohibition to commit suicide applies even to a Gentile. However, other Poskim^[9] rule that gentiles are not included in the command against suicide.]

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^[1] Rambam Hilchos Rotzeiach chapter 2 Halacha 2-4; Gemara Bava Kama 91b; Shach 345:1; See Encyclopedia Talmudit Erech “Miabeid Atzmo Ladaas” Vol. 38

[2] Bereishis 9:5

[3] Rabbeinu Bechaye on Bereishis ibid

[4] Pnei Yehoshua Bava Metziah 59a; Teshuvah Meahavah 3:409; Halef Lecha Shlomo Y.D. 321; Midrash Tehillim 120; Shaul Yosef Daas 345; See Encyclopedia Talmudit ibid footnote 93

[5] Bereishis Raba 34:13

[6] Beis Meir Y.D. 215:5

[7] Minchas Chinuch Mitzvah 34:8

[8] Chasam Sofer Pesachim 53b; Igros Moshe C.M. 2:71; Sefarim in Encyclopedia Talmudit ibid footnote 18.

[9] Minchas Chinuch Mitzvah 34