Muwatta Malik, Book 3, Hadith 217 (In-Book)

Yahya related to me from Malik from Ibn Shihab from al-Araj that Abdullah ibn Buhayna said, "The Messenger of Allah, may Allah bless him and grant him peace, prayed two rakas with us and then stood without sitting and the people stood with him. When he had finished the prayerand we had seen him say the taslim, he said 'Allah is greater' and did two sajdas from the sitting position and then said the taslim again."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنِ الأَعْرَجِ، عَنْ عَبْدِ اللَّهِ ابْنِ بُحَيْنَةَ، أَنَّهُ قَالَ صَلَّى لَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم رَكْعَتَيْنِ ثُمَّ قَامَ فَلَمْ يَجْلِسْ فَقَامَ النَّاسُ مَعَهُ فَلَمَّا قَضَى صَلاَتَهُ وَنَظَرْنَا تَسْلِيمَهُ كَبَّرَ ثُمَّ سَجَدَ سَجْدَتَيْنِ وَهُوَ جَالِسٌ قَبْلَ التَّسْلِيمِ ثُمَّ سَلَّمَ ‏.‏

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also referenced under: Book 3, Hadith 70 (USC-MSA)