«كان إذا نام من الليل أو مرض صلى من النهار اثنتي عشرة ركعة»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) slept through the night (missing his night prayer) or fell ill, he would pray twelve rak'ahs during the day."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4788