Nahj al-Balāgha

Hadith 632
warfare-jihad
ومن كلام له (عليه السلام) وقد استشاره عمر بن الخطاب في الشخوص لقتال الفرس بنفسه
And a saying of his (as) when ‘Umar ibn al-Khaṭṭāb consulted him about taking part himself in fighting the Persians. [1]
Source: al-Sharīf al-Raḍī