بُلُوغُ الْمَرَامِ
Bulugh al-Maram 349
The Book of Prayer
وَعَنْ عَبْدِ اَلرَّحْمَنِ بْنِ عَوْفٍ - رضى الله عنه - قَالَ : { سَجَدَ اَلنَّبِيُّ - صلى الله عليه وسلم -فَأَطَالَ اَلسُّجُودَ , ثُمَّ رَفَعَ رَأْسَهُ وَقَالَ : إِنَّ جِبْرِيلَ آتَانِي , فَبَشَّرَنِي , فَسَجَدْت لِلَّهِ شُكْرًا } رَوَاهُ أَحْمَدُ , وَصَحَّحَهُ اَلْحَاكِمُ . [1]
Narrated 'Abdur-Rahman bin 'Auf (RA): The Prophet (ﷺ) prostrated and prolonged the Sajda, he then raised his head and said, "Jibrael (Gabriel) had come and given me glad tidings, thereafter I prostrated in gratitude to Allah." [Ahmad reported it and al-Hakim graded it Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 250