Sunan Ibn Majah, Volume 2, Book 6, Hadith 1489 (DarusSalam) ⓘ

It was narrated that Kuraib the freed slave of ‘Abdullah bin ‘Abbas said: “A son of ‘Abdullah bin ‘Abbas died, and he said to me: ‘O Kuraib! Get up and see if anyone has assembled (to pray) for my son.’ I said: ‘Yes.’ He said: ‘Woe to you, how many do you see? Forty?’ I said: ‘No, rather there are more.’ He said: ‘Take my son out, for I bear witness that I hear the Messenger of Allah say: “No (group of) forty believers intercede for a believer, but Allah will accept their intercession.”

حَدَّثَنَا إِبْرَاهِيمُ بْنُ الْمُنْذِرِ الْحِزَامِيُّ، حَدَّثَنَا بَكْرُ بْنُ سُلَيْمٍ، حَدَّثَنِي حُمَيْدُ بْنُ زِيَادٍ الْخَرَّاطُ، عَنْ كُرَيْبٍ، مَوْلَى عَبْدِ اللَّهِ بْنِ عَبَّاسٍ قَالَ هَلَكَ ابْنٌ لِعَبْدِ اللَّهِ بْنِ عَبَّاسٍ فَقَالَ لِي يَا كُرَيْبُ قُمْ فَانْظُرْ هَلِ اجْتَمَعَ لاِبْنِي أَحَدٌ فَقُلْتُ نَعَمْ ‏.‏ فَقَالَ وَيْحَكَ كَمْ تَرَاهُمْ أَرْبَعِينَ قُلْتُ لاَ بَلْ هُمْ أَكْثَرُ ‏.‏ قَالَ فَاخْرُجُوا بِابْنِي فَأَشْهَدُ لَسَمِعْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ يَقُولُ ‏ "‏ مَا مِنْ أَرْبَعِينَ مِنْ مُؤْمِنٍ يَشْفَعُونَ لِمُؤْمِنٍ إِلاَّ شَفَّعَهُمُ اللَّهُ ‏" ‏ ‏.‏