Language:
كتاب بدء الخلق
59
Beginning of Creation
(7)
Chapter: If anyone says Amin [during the Salat (prayer) at the end of the recitation of Surat Al-Fatiha]
(7)
بَابُ إِذَا قَالَ أَحَدُكُمْ آمِينَ. وَالْمَلاَئِكَةُ فِي السَّمَاءِ، فَوَافَقَتْ إِحْدَاهُمَا الأُخْرَى، غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ
Sahih al-Bukhari 3232

Narrated Abu 'Is-haq-Ash-Shaibani:

I asked Zir bin Hubaish regarding the Statement of Allah: "And was at a distance Of but two bowlengths Or (even) nearer; So did (Allah) convey The Inspiration to His slave (Gabriel) and then he (Gabriel) Conveyed (that to Muhammad). (53.9-10) On that, Zir said, "Ibn Mas`ud informed us that the Prophet (ﷺ) had seen Gabriel having 600 wings."

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا أَبُو عَوَانَةَ، حَدَّثَنَا أَبُو إِسْحَاقَ الشَّيْبَانِيُّ، قَالَ سَأَلْتُ زِرَّ بْنَ حُبَيْشٍ عَنْ قَوْلِ اللَّهِ، تَعَالَى ‏{‏فَكَانَ قَابَ قَوْسَيْنِ أَوْ أَدْنَى * فَأَوْحَى إِلَى عَبْدِهِ مَا أَوْحَى‏}‏‏.‏ قَالَ حَدَّثَنَا ابْنُ مَسْعُودٍ أَنَّهُ رَأَى جِبْرِيلَ لَهُ سِتُّمِائَةِ جَنَاحٍ‏.‏
Reference : Sahih al-Bukhari 3232
In-book reference : Book 59, Hadith 43
USC-MSA web (English) reference : Vol. 4, Book 54, Hadith 455
  (deprecated numbering scheme)