It wasnarrated that Abu Musa Al-Ash'ari said:
"The Messenger ofAllah(ﷺ) said: 'When the Imam recites, then listen attentively, andifhe is sitting (in the prayer) then the first remembrance thatanyoneof you recites should be the Tashahhud.'" (IT)
English reference (IT): Vol. 1, Book 5, Hadith 847 (IT)
Arabic reference (IT): Book 5, Hadith 896 (IT)