From “Juzz fihi zikri hal Ikrima mawla ibn Abbas” by  Hafidh Munziri.

Munziri said: “Bukhari relied upon his ahadeth in his saheeh, and narrated from him Abu Dawud Sijistane, Abu Isa at-Tirmizi, Abu Abdurrahman an-Nasai, Abu Abdullah ibn Majah al-Qazwini in their books. And his ahadeth were authenticated by Tirmizi”. (p 18, #6).

Bukhari said: “There is no one from our companions who wouldn’t rely on Ikrima” (p 18, #8). Abu Abdurrahman an-Nasai said he was thiqat. (p 18, #9) . When Ayub was asked about him, he said: “If he wouldn’t be thiqat in my view, I wouldn’t record from him”. (p 19, #10). Abdurrahman ibn Abu Hatim asked his father about him, and he said: “He’s thiqat”. I asked: “Would you rely on his ahadeth?” He said: “Yes, if he narrated from thiqat”.  (p 19, #11).  Marwazi said: “I asked Ahmad ibn Hanbal: “Would you rely on ahadeth of Ikrima?”  He said: “Yes, he’s to be relied on”. (p 19, #12).

Abu Abdullah Muhammad ibn Nasr Al-Marwazi said: “Majority of people of knowledge agreed upon, that ahadeth of Ikrima should be relied on. And agreed upon that leaders of ahlal hadith in our time, from them: Ahmad ibn Hanbal, Ishaq ibn Rahaweyh, Abu Thawr, Yahya ibn Maeen. I asked Ishaq ibn Rahaweyh about relying upon ahadeth of Ikrima, he said: “Ikrima in my view is imam of world”, and he surprised from my question to him. And narrated to me more than one man, that when Yahya ibn Maeen was asked about relying upon ahadeth of Ikrima, he showed his astonishment (by such questions)”. (p 21, also see “Tahzib at-tahzib” 7/241)

Shabe said: “No one remained more knowledgeable in book of Allah, than Ikrima”. (p 22, #19).

Yahya ibn Ayub said: Ibn Jurayj said to me: He (Ikrima) came to you in Misr? I said: Yes. He asked: And you wrote from him (ahadeth)? I said: No. He said: 2/3 of knowledge left you. (p 22, #21).

Ali ibn Madene said: “Ikrima was from people of knowledge”. (p 23, #22).

Uthman ibn Hakim said: “Ikrima came to Umama ibn Sahl ibn Hunayf, and I was sitting near him. He asked: “O Abu Umama! Did you hear ibn Abbas saying: “Whatever Ikrima narrated to you from me, confirm him, because he wouldn’t lie upon me?” He answered: “Yes”. (p 23, #24, also see “Tahzib at-tahzib” 7/236).

Qatada said: “Most knowledgeable from people in halal and haram is Hasan, and most knowledgeable in rituals of haj Ata, and most knowledgeable in tafsir Ikrima”. (p 23, #25).

Jabir ibn Ziyad Abu Shatha said: “He is most knowledgeable of people”. (p 24, #26).

Salam ibn Miskin said: “Ikrima is most knowledgeable of people in tafsir”. (p 24).

Sufayn as-Sawri said: “Take tafsir from Ikrima, Saeed ibn Jubayr, Mujahid and Dahhak”.(p 25, #29).

Some info from other books:

Ibn Hajar in “Taqrib” (#4673) said: Thiqat, steady, a`lim bi tafsir, and it’s not proved that he was accused in lie by ibn Umar, and it’s not proved innovation from him”

Ijli said he was thiqat. (“Tahzib at-tahzib” 7/239). Ibn Hibban mentioned him in “Thiqat” and said: “From scholars of his time in fiqh and tafsir”. (“Tahzib at-tahzib” 7/240)

Zirikli in “Alam” (4/244) said: “From most knowledgeable people in tafsir and magazi”.