Zayd ibn Thabit reported: I was sitting to the side of the Prophet, peace and blessings be upon him, one day as the revelation came to him. The Prophet was overcome with calm and his thigh fell upon my thigh as the calm overtook him. By Allah, I have never found anything heavier than the thigh of the Messenger of Allah, then he was released from it. The Prophet said, “Write, O Zayd.” I took a shoulder bone and the Prophet said, “Write: Not equal are those who stay back and those who wage jihad among the believers,” until the end of the verse, “… a great reward,” (4:95). So I wrote that on a shoulder bone.
Source: Musnad Aḥmad 21156
Grade: Sahih (authentic) according to Ahmad Shakir
عَنْ زَيْد بْن ثَابِتٍ قَالَ إِنِّي قَاعِدٌ إِلَى جَنْبِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَوْمًا إِذْ أُوحِيَ إِلَيْهِ قَالَ وَغَشِيَتْهُ السَّكِينَةُ وَوَقَعَ فَخِذُهُ عَلَى فَخِذِي حِينَ غَشِيَتْهُ السَّكِينَةُ قَالَ زَيْدٌ فَلَا وَاللَّهِ مَا وَجَدْتُ شَيْئًا قَطُّ أَثْقَلَ مِنْ فَخِذِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ثُمَّ سُرِّيَ عَنْهُ فَقَالَ اكْتُبْ يَا زَيْدُ فَأَخَذْتُ كَتِفًا فَقَالَ اكْتُبْ لَا يَسْتَوِي الْقَاعِدُونَ مِنْ الْمُؤْمِنِينَ وَالْمُجَاهِدُونَ الْآيَةَ كُلَّهَا إِلَى قَوْلِهِ أَجْرًا عَظِيمًا فَكَتَبْتُ ذَلِكَ فِي كَتِفٍ
21156 مسند أحمد مسند الأنصار رضي الله عنهم
1/558 المحدث أحمد شاكر خلاصة حكم المحدث بإسنادين صحيحين في عمدة التفسير