Language:
كتاب فضائل القرآن
66
Virtues of the Qur'an
(1)
Chapter: How the Divine Revelation used to be revealed and what was the first thing revealed
(1)
باب كَيْفَ نُزُولُ الْوَحْىِ وَأَوَّلُ مَا نَزَلَ
قَالَ ابْنُ عَبَّاسٍ الْمُهَيْمِنُ الأَمِينُ، الْقُرْآنُ أَمِينٌ عَلَى كُلِّ كِتَابٍ قَبْلَهُ.

Narrated Jundub:

Once the Prophet (ﷺ) fell ill and did not offer the night prayer (Tahajjud prayer) for a night or two. A woman (the wife of Abu Lahab) came to him and said, "O Muhammad ! I do not see but that your Satan has left you." Then Allah revealed (Surat-Ad-Duha): 'By the fore-noon, and by the night when it darkens (or is still); Your Lord has not forsaken you, nor hated you.' (93)

حَدَّثَنَا أَبُو نُعَيْمٍ، حَدَّثَنَا سُفْيَانُ، عَنِ الأَسْوَدِ بْنِ قَيْسٍ، قَالَ سَمِعْتُ جُنْدَبًا، يَقُولُ اشْتَكَى النَّبِيُّ صلى الله عليه وسلم فَلَمْ يَقُمْ لَيْلَةً أَوْ لَيْلَتَيْنِ فَأَتَتْهُ امْرَأَةٌ فَقَالَتْ يَا مُحَمَّدُ مَا أُرَى شَيْطَانَكَ إِلاَّ قَدْ تَرَكَكَ، فَأَنْزَلَ اللَّهُ عَزَّ وَجَلَّ ‏{‏وَالضُّحَى * وَاللَّيْلِ إِذَا سَجَى * مَا وَدَّعَكَ رَبُّكَ وَمَا قَلَى‏}
Reference : Sahih al-Bukhari 4983
In-book reference : Book 66, Hadith 5
USC-MSA web (English) reference : Vol. 6, Book 61, Hadith 506
  (deprecated numbering scheme)