Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) relates that one day the Messenger of Allah (peace and blessings be upon him) came out to us while we were teaching one another to recite the Qur'an, and he (peace and blessings be upon him) said: "Praise be to Allah, the Book of Allah is one, and among you are the fair and among you are the black. Recite it before people recite it who will straighten it as an arrow is straightened; each of them will seek its reward hastily and will not defer it."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6000