Musannaf Ibn Abi Shayba 3:3873

Waki’ narrated to us, he said: Sufyan narrated to us, from Qabus ibn Abi Zabyan, from his father, that ‘Umar ibn al-Khattab passed through the mosque and performed one rak’ah. It was said to him, "You only performed one rak’ah." He said, "It is only a voluntary prayer, and I disliked to take it [the mosque] as a thoroughfare."