Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says: I do not feel as much regret over anything as I feel over this: why did I not fight the rebellious group together with Sayyiduna Ali (may Allah be pleased with him)?
Al-Tabarani recorded it with several chains, one of which has narrators who are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الفتن - أعاذنا الله منها / 12054