Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: I asked Bilal (may Allah be pleased with him): Where did the Messenger of Allah (peace and blessings be upon him) pray? He said: "Two rak'ahs between the two pillars."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1048