Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When the iqamah for the prayer is called, do not come running; rather, hold to tranquillity. Pray as much of the prayer as you catch, and complete whatever of the prayer you have missed, for you are in prayer even while you are intending the prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5871