Abdullah says that I said to my father, Imam Ahmad: I heard Abu Khaythamah saying that the narrator Nasr bin Bab is a liar. Upon this, he said "Astaghfirullah" and began to express astonishment, saying "a liar?" The only reason the hadith scholars have criticized him is that he narrated hadith from Ibrahim al-Saigh, and Ibrahim al-Saigh is from the people of his city, so hearing (hadith) from him is not something surprising.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14331M