Is a hadith that was narrated by trustworthy imams all the way to the core of the hadith, and then narrated by weak narrators thereafter, considered sound or weak?

For a Hadith (definition) to be authenticated, the conditions of authenticity must be met in all layers of its chain of narration (isnad (definition)), as Imam Al-Shafi'i stated. If the Hadith's chains of narration revolve around a trustworthy narrator, but those who narrated from him are weak, the Hadith can be strengthened by corroborating narrations (mutaba'at), where the Hadith is narrated through other chains, or by a different Companion (witness/shawahid). Weakness in narrators is overlooked in corroborating narrations and witnesses if their weakness is not due to disqualifying factors such as lying. It is also imperative to verify the authenticity of the chain for the corroborating narrations and ensure they are not anomalous, because some severe weaknesses, like being accused of lying or being anomalous, are not removed by corroborating narrations. Valid corroborating narrations are those that lead to a strong presumption that the narrators were accurate in their transmission.