Narrated Ibn Masud: We used to fight in the holy battles in the company of the Prophet and we had no wives with us. So we said, "O Allah's Apostle! Shall we get castrated?" The Prophet forbade us to do so.

Narrated `Abdullah: We used to participate in the holy wars carried on by the Prophet and we had no women (wives) with us. So we said (to the Prophet). "Shall we castrate ourselves?" But the Prophet forbade us to do that and thenceforth he allowed us to marry a woman (temporarily) by giving her even a garment, and then he recited: "O you who believe! Do not make unlawful the good things which Allah has made lawful for you."

Narrated Abu Huraira: I said, "O Allah's Apostle! I am a young man and I am afraid that I may commit illegal sexual intercourse and I cannot afford to marry." He kept silent, and then repeated my question once again, but he kept silent. I said the same (for the third time) and he remained silent. Then repeated my question (for the fourth time), and only then the Prophet said, "O Abu Huraira! The pen has dried after writing what you are going to confront. So (it does not matter whether you) get yourself castrated or not."

Narrated Sahl: I heard the Prophet saying, "A (small) place equal to an area occupied by a whip in Paradise is better than the (whole) world and whatever is in it; and an undertaking (journey) in the forenoon or in the afternoon for Allah's Cause, is better than the whole world and whatever is in it."