If the chain is considered by someone as weak or broken or unauthentic the wordings itself are so beautiful that to deny it due to any narration doubt is impossible just like dua e Sabah. Secondly asking help of Amir ul momineen a.s.is in itself as asking Allah s.w.t. as he is among the most humble Servants of Allah s.w.t.
Thirdly it is narrated that Holy Prophet s.a.w.w. had uttered these wordings during the battle of Khyber.