Al-Qasim ibn Abi Ayyub reported: When Sa’id ibn Jubayr, may Allah be pleased with him, reached the first ten days of Dhul-Hijjah, he would exert himself in worship so greatly that he would nearly overwhelm himself.
Source: Sunan al-Dārimī 1774
عَنْ الْقَاسِمِ بْنِ أَبِي أَيُّوبَ وَكَانَ سَعِيدُ بْنُ جُبَيْرٍ رضي الله عنه إِذَا دَخَلَ أَيَّامُ الْعَشْرِ اجْتَهَدَ اجْتِهَادًا شَدِيدًا حَتَّى مَا يَكَادُ يَقْدِرُ عَلَيْهِ
1774 سنن الدارمي كتاب الصوم باب في فضل العمل في العشر