Hadithcore
Sahih Muslim, 174 c
sahih

Zirr b. Hubaish narrated it on the authority of 'Abdullah (that the words of Allah):

" Certainly he saw of the greatest signs of Allah" (al-Qur'an, liii. 18) imply that he saw Gabriel in his (original) form and he had six hundred wings.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ الْعَنْبَرِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ سُلَيْمَانَ الشَّيْبَانِيِّ، سَمِعَ زِرَّ بْنَ حُبَيْشٍ، عَنْ عَبْدِ اللَّهِ، قَالَ ‏{‏ لَقَدْ رَأَى مِنْ آيَاتِ رَبِّهِ الْكُبْرَى‏}‏ قَالَ رَأَى جِبْرِيلَ فِي صُورَتِهِ لَهُ سِتُّمِائَةِ جَنَاحٍ ‏.‏

References2 variants
In-Book Reference
Book 1, Hadith 339
USC-MSA web (English) reference
Book 1, Hadith 332 (deprecated numbering scheme)