مُوَطَّأُ مَالِكٍ
Muwatta Malik 398
Shortening the Prayer
حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي أُمَامَةَ بْنِ سَهْلِ بْنِ حُنَيْفٍ، أَنَّهُ قَالَ دَخَلَ زَيْدُ بْنُ ثَابِتٍ الْمَسْجِدَ فَوَجَدَ النَّاسَ رُكُوعًا فَرَكَعَ ثُمَّ دَبَّ حَتَّى وَصَلَ الصَّفَّ .
Yahya related to me from Malik from Ibn Shihab that Abu Umama ibn Sahl ibn Hunayf said, "Zayd ibn Thabit entered the mosque and found the people in ruku, so he went into ruku and then moved slowly forward until he reached the row."
Arabic/English book reference: Book 9, Hadith 67