Musnad Ahmad 30:544

'Abd al-Razzaq narrated to us, from Ma'mar, who said: Al-Zuhri said: Sa'id ibn al-Musayyib informed me, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When the prayer is established, do not come to it running, but come to it walking, and upon you is tranquility. So whatever you catch, pray, and whatever you miss, complete."