Maliks Muwatta Book 9, Hadith Number 21.

Section : The Prayer of a Traveller when Imam, or Behind an Imam.

Yahya related to me from Malik from Ibn Shihab from Salim ibn Abdullah from his father that Umar ibn al-Khattab, when he went to Makka, used to lead them in prayer and do two rakas and then say, “People of Makka, complete the prayer, we are a group travelling.”

Yahya related the same as that to me from Malik from Zayd ibn Aslam from his father from Umar ibn al-Khattab.