Yahya related to me from Malik from Amir ibn Abdullah ibn az-Zubayr from Amr ibn Sulaymaz-Zuraqi from Abu Qatadaal-Ansari that theMessenger of Allah, may Allah bless him and grant him peace, said,"When you enter the mosque, you should pray two rakas before you sitdown." (PT)
USC-MSA web (English) reference: Book 9, Hadith 60 (PT)
Arabic reference (PT): Book 9, Hadith 391 (PT)