Saaib bin Yazid reported,

Umar gathered the people during Ramadan to pray behind Ubayy bin Kaab and Tamim Dari, performing twenty-one rakahs. They would recite from the surahs containing a hundred verses or more, and they would finish as dawn was breaking.

Azami 4648

Sahih

عن السائب بن يزيد

أن عمر جمع الناس في رمضان على أبي بن كعب، وعلى تميم الداري على إحدى وعشرين ركعة، يقرؤون بالمئين، وينصرفون عند فروع الفجر.

الأعظمي 4648صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Fasting
Chapter
Night prayer in Ramadan
Section
Number of rakaat in the night prayer in Ramadan
Numbering
Jami al-Kamil 4648 (2nd edition)
Azami 4648