Musnad Ahmad 26:436

Muhammad ibn Ubayd narrated to us, Isma'il narrated to us, from Qays, from Abdullah, who said: We used to go on military expeditions with the Messenger of Allah, may Allah bless him and grant him peace, and we did not have our wives with us. So we said: "O Messenger of Allah, shall we not castrate ourselves?" He forbade us from that. Then, he later permitted us to marry a woman for a garment for a specified term. Then Abdullah recited: "O you who have believed, do not prohibit the good things which Allah has made lawful to you and do not transgress. Indeed, Allah does not like transgressors." [Al-Ma'idah: 87]