Abu Ahmad ibn Adi al-Jurjani: He has many hadiths, straight, God willing, all of them. The Imams narrated from him, and he is one of the prominent followers of the Kufis. His hadiths from those he narrated from are good, and he is truthful, there is nothing wrong with him.
Abu Ishaq as-Sabi'i: Take knowledge from Sumakh ibn Harb. And once: You should follow 'Abd al-Malik ibn Umair and Sumakh ibn Harb
Abu Bakr al-Bazzar: A famous man, I don't know anyone who abandoned him, he changed before his death
Abu Hatim al-Razi: Truthful, trustworthy
Abu Hatim ibn Hibban al-Busti: Makes many mistakes
Ahmad ibn Hanbal: Sumakh is more accurate in hadith than 'Abd al-Malik ibn Umair. And once: Confused in hadith. And once: He was asked about Sumakh ibn Harb and 'Ata' ibn al-Sa'ib, so he said, 'How close they are!'
Ahmad ibn Shu'ayb al-Nasai: There is nothing wrong with him, but there is something in his hadith. And once he mentioned him in al-Sunan al-Sughra and said: 'He is not strong.'
Ahmad ibn Salih al-Jalil: His hadith is acceptable, except that there was something in the hadith of Ikrimah that he connected to Ibn 'Abbas. No one abandoned his hadith.
Ibn Hajar al-'Asqalani: If he was truthful, he may have been prompted, so if he narrated alone from an origin, he was not a proof. His narration from Ikrimah in particular is confusing, and he changed later in life, so he may have been prompted.
Al-Daraqutni: Poor memory
Al-Dhahabi: Trustworthy, his memory deteriorated, one of the flags of Kufa
Jarir ibn 'Abd al-Hamid al-Dubi: I came to him and found him urinating standing, so I left him and did not hear from him
Hammad ibn Zayd al-Jahadmi: I heard him say: I caught eighty of the companions of Muhammad, may God bless him and grant him peace.
Sufyan al-Thawri: He was considered weak by some. And once: Weak. And once: No hadith of Sumakh ibn Harb has fallen.
Shu'bah ibn al-Hajjaj: He considered him weak, and he would not narrate his interpretation except from Ikrimah. And once: People used to prompt him, so they would say about Ibn Abbas, 'Is it so?' He would say, 'Yes.' As for me, I did not prompt him. And once: He criticized him.
Salih ibn Muhammad Jazrah: He weakens him.
Abd al-Rahman ibn Yusuf ibn Kharash: There is leniency in his hadith
Muhammad ibn 'Abdullah al-Makhrami: Weak in hadith. And Ya'qub ibn Shaybah's statement about him is only what we see from those who heard from him later in life.
Muhammad ibn 'Ubayd al-Kindi: He used to sit with al-Shu'bi and recite poetry. When the hadith scholars came, he would say, 'The boring ones have come.'
Muhammad ibn 'Amr al-Mawsili: They say he used to make mistakes, and they differed about his hadith.
Yahya ibn Ma'in: Trustworthy, he criticized him for attributing hadiths that no one else attributed.
Ya'qub ibn Sufyan al-Faswi: Confused
Ya'qub ibn Shaybah as-Sadusi: Acceptable, but not among the most reliable. His narration from Ikrimah is confusing, but he is acceptable in other than Ikrimah. Those who heard from him earlier, like Sufyan and Shu'bah, their hadith from him is sound and straight.