That the Messenger of Allah (ﷺ) said: "War is deceit."

There are narrations on this topic from 'Ali, Zaid bin Thabit, 'Aishah, Ibn 'Abbas, Abu Hurairah, Asma' bint Yazid bin As-Sakan, Ka'b bin Malik and Anas bin Malik. This Hadith is Hasan Sahih.
Jami` at-Tirmidhi Book 23, Hadith 6
← Previous Hadith From his father, from his grandfather that the Messenger of Allah (ﷺ) said: "The (lone) rider is a Shaitan, and two raiders are two Shaitan. Three is a travelling party.

The Hadith of Ibn 'Umar (no, 1673) is Hasan Sahih. We do not know of it except from this route ; as a narration of 'Asim. And he is Ibn Muhammad bin Zaid bin 'Abdullah bin 'Umar.

Muhammad said: "He is trustworthy, truthful. And 'Asim bin 'Umar Al-'Umari is weak in Hadith, I do not report anything from him." The Hadith of 'Abdullah bin 'Amr (no. 1674) is better.

Jami` at-Tirmidhi Book 23, Hadith 5 Next Hadith → "I was next to Zaid bin Arqam when he was asked: 'How many battles did the Prophet (ﷺ) fight ?' He said: 'Nineteen.' So I said: 'How many battles did you take part in with him ?' he said: 'Seventeen.' I said: 'Which of them was the first?' He said: 'Dhat Al-Ushaira' or Al-'Usaira'. '"

This Hadith is Hasan Sahih.

Jami` at-Tirmidhi Book 23, Hadith 7