The following text was collected form the net. It explains in details, with references, the reliability of Nuaim bin Hammad.
About reliability of Imam Nuaim bin hammad there is ikhtilaaf among scholars of Jarh wa tadeel. Jumhoor have declared him trustworthy and hasan-ul-hadith and some have made Tadeel- Mufassar on him.
The author of six books reported from him.
1. Imam Bukhari
Reported hadith from him in his sahih. [vol-1 p-38 h 246], [vol-1 p-56 h 392] [vol-1 p-529 h 3736] [vol-p-543 h 3849 ] and other places.
2. Imam Muslim
In muqaddimah [vol-1 pg-17] of his sahih.
3. Imam Yahya ibn Maeen
Said "thiqah" [sawalat ibn junaid p-398] and in p-399 of same book Ibn Maeen said: He was my companion in basrah. Both of these narrations from Ibn Maeen is based on sahih Isnaad.
4. Imam Tirmidhi
Declared his hadith to be 'Sahih Ghareeb'.
[Jami-ut-Tirmidhi with Tuhfadul Ahwadhee Vol-3 P-17]
If any Muhaddith declares any hadith to be Sahih then he considers all its narrators to be trustworthy.
[see Al-Iqtiraah of Ibn Daqiq Al-eid pg-55,Nasb-ur-rayah of zailée vol-3 p-264]
5. Imam al-mu'tadil al- Ajli
Said: Thiqah [tarikh thiqaat al-ajli p-451]
Some of the scholars from 14th century have misconception that Imam Al-Ajli was mutasaahil. This claim is false from Many angles.
a) Imam Abbas ibn MUhammad Ad-Duree
Considered him to be equivalent to Imam Ahmad Ibn Hanbal and Imam Yahya ibn Maeen.[Tarikh Baghdad 4/214 with sahih sanad]
b) Imam Yahya ibn Maeen
Said "he is thiqah,his father is thiqah and his grandfather is thiqah"[tarikh baghdad 4/215 with sahih sanad]
c) Thiqah Imam Waleed ibn Bakr al-andalusi
Decalred him Hafidh like Ibn Maeen [tarikh baghdad 4/215 with sahih sanad]
d) No one of Mutaqaddimeen Muhaddith declared him to be Mutasaahil.
6. Abu Hatim Ar-Razee
Declared him Sudooq [Al- jarh wa tadeel vol-8 p-464]
7-Imam Ibn Hibban
Mentioned him in At-Thiqaat [vol-9 p-219]
He also took his hadith in Sahih Ibn Hibban [al-ihsaan 341]
8. Imam Haakim
Declared his Hadith to be Sahih [Mustadrak vol-4 p-145]
If any Muhaddith declares any hadith to be Sahih then he considers all its narrators to be trustworthy.
[see Al-Iqtiraah of Ibn Daqiq Al-eid pg-55,Nasb-ur-rayah of zailée vol-3 p-264]
9. Imam Dhahabi
Declared singular narration of Nuaim to be sahih. [ talkhees Mustadrak vol-4 p-145]
10. Al-Haythami
Said "Thiqah" [majm az-zawaid vol-9 p-347]
11. Imam Ahmad ibn Hanbal
Declared him Thiqah. [Al-kaamil Ibn Adee vol-7 p-2482,Meezan Al-itidaal vol-4 p-267,Siyaar Alam An-Nubala vol-10 p-597,tahzeeb at-tahzeeb,Tahzeeb al-kamal]
There is doubt regarding this narration but its supported by some other statements of Imam Ahmad.
Imam Ahmad: We call him Nuaim al-faaridh [kitab al-ilal 3/437]
Imam Ahmad:He was greatest scholar of al-faraidh [ tarikh baghdad 13/307 with sahih sanad]
12. Ibn Adee
Said, Except some hadith which are rejected from him,All his hadith are Sahih. [Al-kaamil vol-8 p-2489]
13. Hafidh Ibn Hajr
Said in Taqreeb al-tahzeeb :Sudooq yaqta kaseer.and quoted statement of Ibn Adee.
He said in Tahzeeb a-tahzeeb: Its proved that Nuaim was credible and Trustworthy,but there are some Auhaam in some of narration and Ibn Adee has collected has his Auhaam. [vol-10 p-412,413]
14. Al-kharzaji
In khulasa at-tazheeb tahzeeb al-kamal fee asmaa rijaal quoted verdict of Imam Ahmad,Ibn Maeen and Al-Ajli on him[as mentioned above where they declared him thiqah ]and did not mention any criticism.
15. Karmaani
In his Sharh of sahih bukhari mentioned verdict of Imam Ahmad concerning him and did not accept jarh of few on him. [see vol-3 p-106]
16. Allamah Ainee Hanafi
Mentioned verdict of Imam Ahmad declaring him thiqah and ignored criticism of few on him. [Umdatul qaari vol-1 p-186]
17. Imam An-Nawawi
Declared his hadith to be sahih [Al-Arbaeen 41]
18. Imam Ibn Khuzaymah
Reported from him in his Sahih to establish hujjah. [vol-3 hadith 2236]
19. Ibn Jaarud
Reported from him in Sahih Ibn Jaarud[341] and took istidlaal from it.
20. Imam Abu Awana
Reported from him in Sahih Abi Awaana vol-1 hadith 328
21. Imam Bayhaqi
Reorted hadith from him and declared it Hasan. [sunan kubra 3/410]
22. Imam Tahawi
Took many hadith from him in sharh mushkil athaar and sharh maaniul athaar and did not make jarh on him and made istidlaal from his hadith.
And many others like ziya maqdisi in al-muqtaara and others and took his hadith as sahih.
When jumhoor have declared him thiqah, then criticism of few is rejected.