Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
202. Chapter: On the sunna before and after 'Isha'
1098. Ibn 'Umar said, "I prayed with the Messenger of Allah, may Allah bless him and grant him peace, two rak'ats before Dhuhr and two rak'ats after it, two rak'ats after Jumu'a, two rak'ats after Maghrib, and two rak'ats after 'Isha'." [Agreed upon]
1099. 'Abdullah ibn Mughaffal stated that the Messenger of Allah, may Allah bless him and grant him peace, said, "There is a prayer between the two adhans, there is a prayer between the two adhans," and then the third time he said, "For whoever wishes it." [Agreed upon]