What is the status of Hammaad ibn Salamah in Hadith narrations? I hear that some say that he is a weak narrator? For example, if ‘Ali ibn Zayd Judʻaan narrates from him, is he considered weak?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The books on Hadith narrators' biographies all stated that Hammad ibn Salamah was a trustworthy reporter, a respected scholar, and a devout worshipper; there was no difference of opinion among the scholars in this regard. We do not know of any Hadith scholar classifying him as a weak reporter in general. Rather, they only mentioned that his memory slightly weakened in his old age.

Al-Haafith Ibn Hajar wrote, "Hammaad ibn Salamah was a trustworthy narrator and a devout worshipper; he was the most accurate reporter narrating on the authority of Thaabit. He suffered from weakness of memory near the end of his life." [At-Taqreeb]

Shaykh Al-Albaani wrote in his refutation of those who accused Hammaad ibn Salamah of Ikhtilaat (senility/mental deficiency):

"First: We do not know of any Hadith scholar accusing him of Ikhtilaat; rather, they only said that his memory weakened in his old age. This does not undermine his status as a trustworthy reporter, and this is why Ibn As-Salaah did not list him among the reporters who suffered from Ikhtilaat at the end of his book Muqadimat ʻUloom Al-Hadith, nor did Al-Kayyaal do so in his comprehensive book in this discipline, Al-Kawaakib An-Nayyiraat. (Imam) Muslim accepted his narrations in his book Al-Usool; including his hadith narrated on the authority of Thaabit from Anas which was cited earlier (no. 2592).

Second: Ibn ‘Udday wrote in Thaabit's biography in Al-Kaamil (2/527), 'Reliable and trustworthy reporters narrated his hadiths. The one who narrated from him the most was Hammaad ibn Salamah, who is trustworthy and quite truthful; his narrations are sound and authentic if reported by a trustworthy narrator on his authority. He reported many narrations and he is a trustworthy Muslim. The objections on his narrations are not related to his character; rather, they are related to those narrating on his authority; a group of weak and Majhool (whose trustworthiness cannot be affirmed by Hadith scholars) reporters narrated on his authority.'" [As-Silsilah As-Saheehah, 7/179]

What you mentioned, dear brother, that ʻAli ibn Zayd ibn Judʻaan narrated on the authority of Hammaad ibn Salamah is incorrect. It was the other way around. Hammaad ibn Salamah narrated on the authority of ‘Ali ibn Zayd ibn Judʻaan, who was a weak reporter according to scholars. Al-Haafith ibn Hajar wrote about him, "He was a weak reporter belonging to the fourth Tabaqah (tier) of narrators; he passed away in 31 AH, and it is also said that he died earlier..." [At-Taqreeb]

Allah knows best.