(105) باب التَّخْفِيفِ فِي التَّشَهُّدِ الأَوَّلِ
It was narrated that 'Abdullah bin Mas'ud said:
"In the first two rak'ahs the Prophet (ﷺ) was as if he were on stones heated by fire." (ID)
Reference (ID): Sunan an-Nasa'i 1176 (ID)
In-book reference (ID): Book 12, Hadith 148 (ID)
English translation (ID): Vol. 2, Book 12, Hadith 1177 (ID)