Hadithcore
Al-Adab Al-Mufrad, 984
hasan· Al-Albani

Ibn 'Umar said that al-Agharr (who was a man from Muzayna and had been a Companion of the Prophet) was owed some measures of dates by a man from the Banu 'Amr ibn 'Awf who came to him many times. He said, "I went to the Prophet, (ﷺ), and he sent Abu Bakr as-Siddiq with me." He continues, "Everyone we met greeted us. Abu Bakr said, 'Don't you know that when people give the greeting before us, they have the reward? Give the greeting before them and you will have the reward.'"

حَدَّثَنَا إِسْمَاعِيلُ قَالَ‏:‏ حَدَّثَنِي أَخِي، عَنْ سُلَيْمَانَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ عَبْدِ اللهِ بْنِ أَبِي عَتِيقٍ، عَنْ نَافِعٍ، أَنَّ ابْنَ عُمَرَ أَخْبَرَهُ، أَنَّ الأَغَرَّ، وَهُوَ رَجُلٌ مِنْ مُزَيْنَةَ، وَكَانَتْ لَهُ صُحْبَةٌ مَعَ النَّبِيِّ صلى الله عليه وسلم، كَانَتْ لَهُ أَوْسُقٌ مِنْ تَمْرٍ عَلَى رَجُلٍ مِنْ بَنِي عَمْرِو بْنِ عَوْفٍ، اخْتَلَفَ إِلَيْهِ مِرَارًا، قَالَ‏:‏ فَجِئْتُ إِلَى النَّبِيِّ صلى الله عليه وسلم، فَأَرْسَلَ مَعِي أَبَا بَكْرٍ الصِّدِّيقَ، قَالَ‏:‏ فَكُلُّ مَنْ لَقِينَا سَلَّمُوا عَلَيْنَا، فَقَالَ أَبُو بَكْرٍ‏:‏ أَلاَ تَرَى النَّاسَ يَبْدَأُونَكَ بِالسَّلاَمِ فَيَكُونُ لَهُمُ الأَجْرُ‏؟‏ ابْدَأْهُمْ بِالسَّلاَمِ يَكُنْ لَكَ الأَجْرُ يُحَدِّثُ هَذَا ابْنُ عُمَرَ عَنْ نَفْسِهِ‏.‏

References2 variants
In-Book Reference
Book 42, Hadith 20
English Reference
Book 42, Hadith 984