This hadith, with its chain of transmission, states that he would pray Isha and then retire to his bed, without mentioning the four rakahs. He continued the hadith and said in it that he would pray eight rakahs, making them equal in recitation, bowing, and prostration, not sitting in any of them except in the eighth. He would sit, then stand without saying the salam. He would then pray one rakah as the witr, then say the salam once, raising his voice with it until he woke us up. Then he continued with its meaning.
حدثنا هارون بن عبد الله حدثنا يزيد بن هارون أخبرنا
هذا الحديث بإسناده قال يصلي العشاء ثم يأوي إلى فراشه لم يذكر الأربع ركعات وساق الحديث وقال فيه فيصلي ثماني ركعات يسوي بينهن في القراءة والركوع والسجود ولا يجلس في شيء منهن إلا في الثامنة فإنه كان يجلس ثم يقوم ولا يسلم فيه فيصلي ركعة يوتر بها ثم يسلم تسليمة يرفع بها صوته حتى يوقظنا ثم ساق معناه
Graded as sahih. Ahmad reported it in his Musnad, 6/236, from Yazid bin Harun, through this chain.