Asim bin Damra reported,
Ali 
was asked about the night prayer of the Messenger of Allah ﷺ. He said, "He used to pray sixteen rakahs during the night."
Ahmad 1234
Sahihحدثنا عبد الله حدثني العباس بن الوليد حدثنا أبو عوانة عن أبي إسحاق
عن عاصم بن ضمرة قال
سئل علي رضي الله عنه عن صلاة رسول الله ﷺ قال كان يصلي من الليل ست عشرة ركعة
Its isnad is sahih, and it is an abridgment of 1207, though this text contains an error we do not know the source of. This is his statement, "from the night," which all three manuscript copies agree on, while the correct wording is "from the day," as the hadith has already appeared repeatedly and in detail in some of the narrations. This same error will also occur again at 1240, and then the correct version will follow it right after at 1241. Hadiths 1231-1233 are among the additions of Abdullah bin Ahmad.