Maliks Muwatta Book 6, Hadith Number 4.

Yahya related to me from Malik from Muhammad ibn Yusuf that as-Sa’ib ibn Yazid said, “Umar ibn al-Khattab ordered Ubayy ibn Kab and Tamim ad-Dari to watch the night in prayer with the people for eleven rakas.The reciter of the Qur’an would recite the Mi’in (a group of medium-sized suras) until we would be leaning on our staffs from having stood so long in prayer. And we would not leave until the approach of dawn.”