Sahih Muslim Book 4, Hadith Number 1271.

Chapter : He who came up with the Rak’ah, he in fact came up with the prayer (led in congregation with the Imam).

‘Aisha, the wife of the Apostle (may peace be upon him), said that the Messenger of Allah (may peace be upon him) said the afternoon prayer (at the time) when the sun shone in her apartment and its shadow did not extend beyond her apartment.