The Messenger of Allah ﷺ said, "There is no obligatory prayer except that it is preceded by two units of prayer."
قال رسول الله ﷺ: ما من صلاة مفروضة إلا وبين يديها ركعتان.
No references are available.
Ibn Hibban (2455) and Daraqutni (1046) both narrated it through Uthman bin Saeed Qurashi, who said, Muhammad bin Muhajir (he is the Ansari, the Shami) narrated to us, from Thabit bin Ajlan, from Salim bin Amir Khabairi, from Abdullah bin Zubayr, who said such and such. Its chain is hasan because of Thabit bin Ajlan, for his hadith is hasan.