Sahih Bukhari | Volume 9 | Hadith Number 222

Narrated by Abu Wail
Abu Musa and Abii Mas'ud went to 'Ammar when 'Ali had sent him to Kufa to exhort them to fight (on 'Ali's side). They said to him, "Since you have become a Muslim, we have never seen you doing a deed more criticisable to us than your haste in this matter." 'Ammar said, "Since you (both) became Muslims, I have never seen you doing a deed more criticisable to me than your keeping away from this matter." Then Abu Mas'ud provided 'Ammar and Abu Musa with two-piece outfits to wear, and one of them went to the mosque (of Kufa).