Sayyidah Aishah (may Allah be pleased with her) said that the Prophet (peace and blessings be upon him) prayed Isha, then offered eight rak'ahs standing and two rak'ahs sitting, and prayed two rak'ahs between the adhan and the iqamah, and he (peace and blessings be upon him) never left them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4472