Hadith 4:682
Affan narrated to us, he said: Abd al-Wahid ibn Ziyad narrated to us, he said: al-Hasan ibn Ubayd Allah narrated to us, he said: Ibrahim narrated to us, from al-Aswad, from Aisha, she said: The Messenger of Allah (may Allah bless him and grant him peace) used to exert himself during the ten [days/nights] with an exertion that he did not exert in other than it.
حدثنا عفان قال حدثنا عبد الواحد بن زياد قال حدثنا الحسن بن عبيد الله قال حدثنا إبراهيم عن الأسود عن عائشة قالت كان رسول الله صلى الله عليه وسلم يجتهد في العشر اجتهادا لا يجتهد في غيره