Musnad Ahmad 30:3716

Uthman ibn Umar narrated to us, Malik informed us, from al-Ala’ ibn Abd al-Rahman, from his father, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When the call to prayer is made, do not come to it while you are running. Come to it while you are upon tranquility. Whatever you catch, pray it, and whatever you miss, complete it. For indeed, one of you is in a state of prayer as long as he is intending toward the prayer."