Bishr Ibn Al-Haarith (rahimahullaah) was asked about Imaam Ahmad (rahimahullaah) after the Mehnah, so he said: ”Ibn Hanbal was entered into the bellows (i.e. put to trial just as precious stones are exposed to fire in order to be cleaned) and he exited as red gold (i.e. firm upon his religion, upright, steadfast etc)”.
Source: ‘Seerah As-Salaf As-Saaliheen’ of Al-Asbahaanee (rahimahullaah) Chapter:
A mention of the followers of the followers of the Taa’bi’een 1/1055. (Maktabah Shaamilah)