You will receive seven hundred she-camels in return for it on the Day of Resurrection, all wearing bridles
Authentic hadithعن أبي مسعود رضي الله عنه قال: جاء رجل إلى النبي صلى الله عليه وسلم بناقة مَخْطُومَةٍ، فقال: هذه في سبيل الله، فقال رسول الله صلى الله عليه وسلم : «لك بها يوم القيامة سبعمائة ناقة كلها مخطومة».
Abu Mas‘ūd (may Allah be pleased with him) reported that a man came to the Prophet (may Allah's peace and blessings be upon him) with a she-camel wearing a bridle and said: "This is (a donation) in the cause of Allah." The Messenger of Allah (may Allah's peace and blessings be upon him) said: "You will receive seven hundred she-camels in return for it on the Day of Resurrection, all wearing bridles."
Explanation
This Hadīth encourages spending in the cause of Allah, especially in matters which contribute to the war effort such as horses, she-camels or the like. Allah multiplies the reward for such spending seven hundred times. In the Qur'an, Allah, the Almighty, says: {The example of those who spend their wealth in the way of Allah is like a seed [of grain] which grows seven spikes; in each spike is a hundred grains. And Allah multiplies [His reward] for whom He wills. And Allah is all-Encompassing and Knowing.} When animals are bridled, this enables their owner to control them better. So, it was kind of that man to give bridled she-camels, and as a result Allah rewarded him with seven hundred she-camels, all of which were bridled.
Source · Narrated by Muslim
From the Hadith Encyclopedia (hadeethenc.com).