[Machine] Indeed, this odd number is not obligatory, but it is a good sunnah from the Messenger of Allah ﷺ . Allah is odd and He loves odd numbers. This is the narration of Zuhayr and in another narration by Ath-Thawri, it is mentioned that odd number is not obligatory, but it is a sunnah which the Messenger of Allah ﷺ established.
إِنَّ هَذَا الْوِتْرَ لَيْسَ بِحَتْمٍ وَلَكِنَّهُ سُنَّةٌ حَسَنَةٌ مِنْ رَسُولِ اللهِ ﷺ إِنَّ اللهَ وِتْرٌ يُحِبُّ الْوِتْرَ لَفْظُ حَدِيثِ زُهَيْرٍ وَفِي رِوَايَةِ الثَّوْرِيِّ الْوِتْرُ لَيْسَ بِحَتْمٍ وَلَكِنَّهُ سُنَّةٌ سَنَّهَا رَسُولُ اللهِ ﷺ