All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
What you have heard in that lecture was reported by Ibn An-Najjaar from ‘Ali as stated by As-Suyooti in his book entitled "Al-Jaami’". Besides, Al-Haafith Ibn Hajar said in “At-Talkhees”: “We have narrated in a Juz'u (a booklet which contains a number of Ahaadeeth about a specific subject) a Hadeeth from Abu ‘Ali Ibn Shaathaan from Abu ‘Amr Ibn As-Sammaak from the Hadeeth of ‘Ali Ibn Al-Husayn Ibn ‘Ali, from his grandfather ‘Ali Ibn Abi Taalib who said: “I took for myself the weapons of the Prophet and I noticed on the hilt of his sword the following: "Keep ties with those who cut you off, and do good to those who harmed you, and speak the truth even if it were against your own self."
Ibn Hajar added: “Ibn Ar-Rif’ah said in “Al-Matlab”: "There is an interruption in its chain of narrators but it is supported by the Quranic verse." However, this statement is not incontestable as its chain of narrators includes Al-Husayn Ibn Zayd Ibn ‘Ali, whom Ibn Al-Madeeni and others classified as Dha’eef [weak].”
However, Shaykh Al-Albaani mentioned this Hadeeth in “As-Silsilah As-Saheehah” under number 1911.
Allaah Knows best.