Mustadrak al-Hakim — Hadith 1625

Sayyiduna Nu'man bin Bashir (may Allah be pleased with him) was saying on the pulpit of Hims: We stood (in prayer, tarawih) with the Messenger of Allah (peace and blessings be upon him) in the month of Ramadan on the twenty-third night until a third of the night had passed; then we stood with him (peace and blessings be upon him) on the twenty-fifth night until midnight; then on the twenty-seventh night too we stood with him (peace and blessings be upon him) until midnight, so much so that we began to fear that we would miss the "falah". We used to call it falah, whereas you call it suhur (the pre-dawn meal).
This hadith is sahih (authentic) on the condition of Imam Bukhari, and they did not record it. In this hadith there is clear evidence that holding the tarawih prayer in congregation in the mosques of the Muslims is an established Sunnah, and Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) kept urging Sayyiduna Umar (may Allah be pleased with him) to establish this Sunnah until he formally established it. This is the end of the sahih hadiths in the chapters on fasting which the two Shaykhs did not record. [Beginning of the Book of the Rites of Hajj]