بُلُوغُ الْمَرَامِ
Bulugh al-Maram 506
The Book of Prayer
وَفِي رِوَايَةٍ لِمُسْلِمٍ: { صَلَّى حِينَ كَسَفَتِ اَلشَّمْسُ ثَمَانَ رَكَعَاتٍ فِي أَرْبَعِ سَجَدَاتٍ } [1] .
In a narration of Muslim: "When there was an eclipse of the sun, Allah's Messenger (ﷺ) performed eight bowings with four prostrations (in a two Rak'ah prayer for Eclipse)".
Sunnah.com reference: Book 2, Hadith 436