Official missionary handbook, discusses masturbation.
Church of Jesus Christ of Latter-day Saints. "Missionary Standards for Disciples of Jesus Christ." (2019)
You should avoid any thought or action that would separate you from the Spirit of God. This includes but is not limited to adultery; fornication; same-sex activity; oral sex; arousing sexual feelings; inappropriate touching; sending or receiving messages, images, or videos that are immoral or sexual in nature; masturbation; and viewing or using pornography (see 7.5.3). See For the Strength of Youth (2011), “Repentance,” 28–29, for additional information.