The Prophet ﷺ as saying: The two months of 'Id (festival), Ramadan and Dhu al-Hijjah, are not defective. (Using translation from Abū Dāʾūd 2323)

أَنَّ نَبِيَّ اللَّهِ ﷺ قَالَ «شَهْرَا عِيدٍ لَا يَنْقُصَانِ رَمَضَانُ وَذُو الْحِجَّةِ»