Sunan Abu Dawood 961
(There is another chain) from Yahya bin Sa'eed that Al-Qasim bin Muhammad saw them sitting in Tashah-hud, so he mentioned the Hadith.
حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّ الْقَاسِمَ بْنَ مُحَمَّدٍ، أَرَاهُمُ الْجُلُوسَ فِي التَّشَهُّدِ فَذَكَرَ الْحَدِيثَ .
Classification
Sahih (Authentic) [Al-Albani]
References
Sunan Abu Dawood 961
Sunan Abu Dawood Vol. 1, Book of Prayer (Kitab Al-Salat), Hadith 957d