Sayyiduna Ali (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) used to offer two rak'ahs after every obligatory prayer except Fajr and Asr. These are the words of the narration of Waki'.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب صلاة التطوع قبل الصلوات المكتوبات وبعدهن / 1196