Jami` at-Tirmidhi Book 47, Hadith 354
“The Messenger of Allah ordered burning and cutting down the date palms of Banu An-Nadir, and that (place was called Al-Buwairah. So Allah revealed: What you cut down of the Linah, or you left of them standing on their trunks, it was by the leave of Allah, and in order that He might disgrace the rebellious.”
A Jew came to the Prophet of Allah and his Companions and said: “As-Samu Alaikum (Death be upon you).” So the people replied to him. The Prophet of Allah said: “Do you know what this person said?” They said: “Allah and His Messenger know better – he said the Salam – O Allah’s Prophet.” He said: “No, rather he said like this and that. Bring him back for e=me.” So they brought him back and he said: “Did you say As-Samu Alaikum? He said: “Yes.” So with that Allah’s Prophet said: “When one of the People of the Book gives you the Salam, then say: “Alaika Ma Qulta (Whatever you said to you too).” He said: ‘And when they come to you, they greet you with a greeting wherewith Allah greets you not.’
“Habib bin Abi Amrah narrated to us, from Sa’eed bin Jubair, from Ibn Abbas, regarding the saying of Allah, the Mighty and Sublime: What you cut down of the Linah, or you left of them standing on their trunks – he said: ‘The Linah is the date-palms.’ That He might disgrace the rebellious. He said: ‘They were forced from their forts.’ And they were ordered to cut down the date-pals, that caused some hesitation in their chests, so the Muslims said: “We cut some of them, and we left some of them, so let us ask the Messenger of Allah is we are to be rewarded for those that we cut down, and if we will be burdened for what we left?” So Allah revealed the Ayah: What you cut down of the Linah, or you left of them standing on their trunks.”