Musannaf Ibn Abi Shayba 3:4709

Waki’ narrated to us, from Mis’ar, from al-‘Abbas ibn Dharih, from Ibn ‘Abbas, who said: The likeness of the one who enters the mosque when prayer has already been performed in it, then performs a voluntary prayer, is like the likeness of the one who performs ‘Umrah before he performs Hajj.