Mishkat al-Masabih 1496
Sa‘d b. Abu Waqqas said :
We went out with God’s Messenger from Mecca making for Medina, and when we were near ‘Azwaza’* he alighted, then raised his hands and made supplication to God for a time, after which he prostrated himself, remaining a long time in prostration. Then he stood up and raised his hands for a time, after which he prostrated himself, remaining a long time in prostration. Then he stood up and raised his hands for a time, after which he prostrated himself. He then said, “I begged my Lord and made intercession for my people, and He gave me a third of my people, so I prostrated myself in gratitude to my Lord. Then I raised my head and begged my Lord for my people and He gave me a third of my people, so I prostrated myself in gratitude to my Lord. Then I raised my head and begged my Lord for my people and He gave me the last third, so I prostrated myself in gratitude to my Lord.” 

*The name is spelt either as here with the alif mamduda , or with the alif maqsura (i.e. Azwaza). The reference is to a pass in the hills.

Ahmad and Abu Dawud transmitted it.
وَعَن سعد بن أبي وَقاص قَالَ: خَرَجْنَا مَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نم مَكَّةَ نُرِيدُ الْمَدِينَةَ فَلَمَّا كُنَّا قَرِيبًا مِنْ عَزْوَزَاءَ نَزَلَ ثُمَّ رَفَعَ يَدَيْهِ فَدَعَا اللَّهَ سَاعَةً ثُمَّ خَرَّ سَاجِدًا فَمَكَثَ طَوِيلًا ثُمَّ قَامَ فَرَفَعَ يَدَيْهِ سَاعَةً ثُمَّ خَرَّ سَاجِدًا فَمَكَثَ طَوِيلًا ثُمَّ قَامَ فَرَفَعَ يَدَيْهِ سَاعَةً ثُمَّ خَرَّ سَاجِدًا قَالَ: «إِنِّي سَأَلْتُ رَبِّي وَشَفَعْتُ لِأُمَّتِي فَأَعْطَانِي ثُلُثَ أُمَّتِي فَخَرَرْتُ سَاجِدًا لِرَبِّي شُكْرًا ثُمَّ رَفَعْتُ رَأْسِي فَسَأَلْتُ رَبِّي لِأُمَّتِي فَأَعْطَانِي ثُلُثَ أُمَّتِي فَخَرَرْتُ سَاجِدًا لِرَبِّي شُكْرًا ثُمَّ رَفَعْتُ رَأْسِي فَسَأَلْتُ رَبِّي لِأُمَّتِي فَأَعْطَانِي الثُّلُثَ الْآخِرَ فَخَرَرْتُ سَاجِدًا لِرَبِّي شُكْرًا» . رَوَاهُ أَحْمد وَأَبُو دَاوُد