بُلُوغُ الْمَرَامِ
Bulugh al-Maram 511
The Book of Prayer
وَعَنْهُ: { أَنَّهُ صَلَّى فِي زَلْزَلَةٍ سِتَّ رَكَعَاتٍ, وَأَرْبَعَ سَجَدَاتٍ, وَقَالَ: هَكَذَا صَلَاةُ اَلْآيَاتِ } رَوَاهُ اَلْبَيْهَقِيُّ [1] .
Narrated [Ibn 'Abbas (RA)]: He [the Prophet (ﷺ)] prayed during an earthquake six bowings and four prostrations, and said, "This is the way the Prayer of the Signs (of Allah) is offered. [Reported by al-Baihaqi].
Sunnah.com reference: Book 2, Hadith 441