Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1986
'Amr b. al-'As reported: When the sun eclipsed during the lifetime of the Messenger of Allah (may peace be upon him), they (the people) were called to congregational prayers. The Messenger of Allah (may peace be upon him) observed two ruku's in one rak'ah. He then stood and observed two ruku's in (the second) rak'ah. The sun then became bright, and 'A'isha said; Never did I observe, ruku' and prostration longer than this (ruku' and prostration).