وَيَقْرَأُ فِي كُلِّ رَكْعَةٍ مِنَ الْوِتْرِ فَاتِحَةَ الْكِتَابِ وَسُورَةً مَعَهَا.
Meaning: In each rakah of Witr he recites al-Fatihah and an additional surah.
“In every rakah” covers all three: the third is not treated like the later rakahs of an ordinary four-rakah fard prayer.