Sahih Muslim Book 4, Hadith Number 1281.

Chapter : He who came up with the Rak’ah, he in fact came up with the prayer (led in congregation with the Imam).

Abu Musa reported on the authority of his father that an Inquirer came to the Prophet (may peace be upon him) and asked him about the times of prayers, and the rest of the Hadith is the same (as narrated above) but for these words: “On the second day he (the Holy Prophet) observed the evening prayer before the disappearance of the twilight.”