كتاب صلاة الليل
7  
Tahajjud

Yahya related to me from Malik that he had heard that Abdullah ibn Umar used to say, "(Voluntary) prayer in both the day and night is two at a time with a taslim after every 2 raka'ahs."

Malik said, "That is the custom among us."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ صَلاَةُ اللَّيْلِ وَالنَّهَارِ مَثْنَى مَثْنَى يُسَلِّمُ مِنْ كُلِّ رَكْعَتَيْنِ ‏.‏
Sunnah.com reference : Book 7, Hadith 7
USC-MSA web (English) reference : Book 7, Hadith 7
Arabic reference : Book 7, Hadith 261