Arabic hadith text
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، أَنَّ سَعْدَ بْنَ أَبِي وَقَّاصٍ، كَانَ يُوتِرُ بَعْدَ الْعَتَمَةِ بِوَاحِدَةٍ ‏.‏ قَالَ مَالِكٌ وَلَيْسَ عَلَى هَذَا الْعَمَلُ عِنْدَنَا وَلَكِنْ أَدْنَى الْوِتْرِ ثَلاَثٌ ‏.‏
Translation

Yahya related to me from Malik from Ibn Shihab that Sad ibn AbiWaqqas used to pray witr after isha with one raka.

Maliksaid, "This is not the situation with us. Rather three is the minimumfor witr."