كتاب الإيمان
1  
The Book of Faith
(86)
Chapter: The Prophet (saws) will defer his supplication in order to intercede for his ummah
(86)
باب اخْتِبَاءِ النَّبِيِّ صلى الله عليه وسلم دَعْوَةَ الشَّفَاعَةِ لأُمَّتِهِ ‏‏
Sahih Muslim 199 a

Abu Huraira said:

The Prophet of Allah (ﷺ) said: There is for every apostle a prayer which is granted, but every prophet showed haste in his prayer. I have, however, reserved my prayer for the intercession of my Ummah on the Day of Resurrection, and it would be granted, if Allah so willed, in case of everyone amongst my Ummah provided he dies without associating anything with Allah.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ - وَاللَّفْظُ لأَبِي كُرَيْبٍ - قَالاَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ لِكُلِّ نَبِيٍّ دَعْوَةٌ مُسْتَجَابَةٌ فَتَعَجَّلَ كُلُّ نَبِيٍّ دَعْوَتَهُ وَإِنِّي اخْتَبَأْتُ دَعْوَتِي شَفَاعَةً لأُمَّتِي يَوْمَ الْقِيَامَةِ فَهِيَ نَائِلَةٌ إِنْ شَاءَ اللَّهُ مَنْ مَاتَ مِنْ أُمَّتِي لاَ يُشْرِكُ بِاللَّهِ شَيْئًا ‏"‏ ‏.‏
Reference : Sahih Muslim 199a
In-book reference : Book 1, Hadith 397
USC-MSA web (English) reference : Book 1, Hadith 389
  (deprecated numbering scheme)