Sahih Al Bukhari (128)

حَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ: حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ، قَالَ: حَدَّثَنِي أَبِي، عَنْ قَتَادَةَ، قَالَ: حَدَّثَنَا أَنَسُ بْنُ مَالِكٍ أَنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ، وَمُعاذٌ رَدِيفُهُ عَلَى الرَّحْلِ، قَالَ: "يَا مُعَاذَ بْنَ جَبَلٍ"، قَالَ: لَبَّيْكَ يَا رَسُولَ اللَّهِ وَسَعْدَيْكَ، قَالَ: "يَا مُعَاذُ"، قَالَ: لَبَّيْكَ يَا رَسُولَ اللَّهِ وَسَعْدَيْكَ ثَلاَثًا، قَالَ: "مَا مِنْ أَحَدٍ يَشْهَدُ أَنْ لاَ إِلَهَ إِلَّا اللَّهُ وَأَنَّ [ص:38] مُحَمَّدًا رَسُولُ اللَّهِ، صِدْقًا مِنْ قَلْبِهِ، إِلَّا حَرَّمَهُ اللَّهُ عَلَى النَّارِ"، قَالَ يَا رَسُولَ اللَّهِ: أَفَلاَ أُخْبِرُ بِهِ النَّاسَ فَيَسْتَبْشِرُوا؟ قَالَ: "إِذًا يَتَّكِلُوا" وَأَخْبَرَ بِهَا مُعَاذٌ عِنْدَ مَوْتِهِ تَأَثُّمًا

Anas ibn Malik (may Allah be pleased with him) narrated: "Once Mu`adh was along with Allah's Messenger (peace be upon him) as a companion rider. Allah's Messenger (peace be upon him) said: "O Mu`adh ibn Jabal." Mu`adh replied: "Labbayka and Sa`dayka. O Allah's Messenger!" Again the Prophet (peace be upon him) said: "O Mu`adh!" Mu`adh said thrice, "Labbayka and Sa`dayka, O Allah's Messenger!" Allah's Messenger (peace be upon him) said: "There is none who testifies sincerely that none has the right to be worshipped but Allah and Muhammad (peace be upon him) is His Messenger, except that Allah, will save him from the Hell-fire." Mu`adh said: "O Allah's Messenger (peace be upon him)! Shall I inform the people about it so that they may have glad tidings?" He replied: "When the people hear about it, they will solely depend on it." Then Mu`adh narrated the above-mentioned Hadith just before his death, being afraid of committing sin (by not telling the knowledge).