Sahih Bukhari Volume 2, Book 23, Hadith 1288

فَقَالَ ابْنُ عَبَّاسٍ ـ رضى الله عنهما ـ قَدْ كَانَ عُمَرُ ـ رضى الله عنه ـ يَقُولُ بَعْضَ ذَلِكَ، ثُمَّ حَدَّثَ قَالَ صَدَرْتُ مَعَ عُمَرَ ـ رضى الله عنه ـ مِنْ مَكَّةَ حَتَّى إِذَا كُنَّا بِالْبَيْدَاءِ، إِذَا هُوَ بِرَكْبٍ تَحْتَ ظِلِّ سَمُرَةٍ فَقَالَ اذْهَبْ، فَانْظُرْ مَنْ هَؤُلاَءِ الرَّكْبُ قَالَ فَنَظَرْتُ فَإِذَا صُهَيْبٌ، فَأَخْبَرْتُهُ فَقَالَ ادْعُهُ لِي‏.‏ فَرَجَعْتُ إِلَى صُهَيْبٍ فَقُلْتُ ارْتَحِلْ فَالْحَقْ أَمِيرَ الْمُؤْمِنِينَ‏.‏ فَلَمَّا أُصِيبَ عُمَرُ دَخَلَ صُهَيْبٌ يَبْكِي يَقُولُ وَاأَخَاهُ، وَاصَاحِبَاهُ‏.‏ فَقَالَ عُمَرُ ـ رضى الله عنه ـ يَا صُهَيْبُ أَتَبْكِي عَلَىَّ وَقَدْ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّ الْمَيِّتَ يُعَذَّبُ بِبَعْضِ بُكَاءِ أَهْلِهِ عَلَيْهِ ‏"

Ibn Abbas said, "Umar used to say so." Then he added narrating, "I accompanied Umar on a journey from Mecca till we reached Al-Baida. There he saw some travellers in the shade of a Samura (A kind of forest tree). He said (to me), "Go and see who those travellers are." So I went and saw that one of them was Suhaib. I told this to 'Umar who then asked me to call him. So I went back to Suhaib and said to him, "Depart and follow the chief of the faithful believers." Later, when 'Umar was stabbed, Suhaib came in weeping and saying, "O my brother, O my friend!" (on this 'Umar said to him, "O Suhaib! Are you weeping for me while the Prophet said, "The dead person is punished by some of the weeping of his relatives?"