It is narrated from Sayyidah Aishah (may Allah be pleased with her) that when revelation came down upon the Prophet (peace and blessings be upon him) while he (peace and blessings be upon him) was riding his she-camel, she would rest her neck on the ground (from the weight of the revelation) and would not have the strength to move. Then she recited the saying of Allah, the Mighty and Majestic: "Indeed, We will cast upon you a weighty word" [Al-Muzzammil: 5] . This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.