(a) Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When the prayer has started, do not come running, but come walking with calm and tranquillity; whatever you catch, pray it, and whatever you have missed, complete it."
(b) In another narration: "Make up what has been prayed before you came."
The narration of (Ibrahim bin Sa'd,) his son, from him (Sa'd bin Ibrahim), together with al-Zuhri's corroboration of it, is more correct.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3624