Contrary to the claim of the person who says that in every rak'ah of a voluntary prayer, reciting less than three verses in addition to Surah Al-Fatihah will not suffice.

Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that the Messenger of Allah (peace be upon him) would often recite this verse (till the end) in the two (Sunnah) rak‘ahs of Fajr: «‏‏‏‏قُولُوا آمَنَّا بِاللَّهِ وَمَا أُنزِلَ إِلَيْنَا وَمَا أُنزِلَ إِلَىٰ إِبْرَاهِيمَ» ‏‏‏‏ "Say, 'We believe in Allah and in what has been sent down to us and what was sent down to Ibrahim...'" till the end of the verse [ سوره البقرۃ: 136 ] and in the second rak‘ah he would recite this verse «‏‏‏‏قُلْ يَا أَهْلَ الْكِتَابِ تَعَالَوْا إِلَىٰ كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ۔۔۔ اشْهَدُوا بِأَنَّا مُسْلِمُونَ» ‏‏‏‏ [ سورة آل عمران: 64 ] "Say, 'O People of the Book, come to a word that is equitable between us and you...'" till "bear witness that indeed we are Muslims (submitting to Allah)."