How accurate is the phrase: "O Allah, I have conveyed; O Allah, therefore bear witness"?

"Have I not conveyed? O Allah, be my witness," is part of an authentic Hadith (definition) narrated by Al-Bukhari, Muslim, and others, where the Prophet, peace and blessings be upon him, said it in his sermon on the Day of Sacrifice after mentioning the sanctity of blood and property. He then commanded that those present convey the message to those absent. Other narrations also exist with the wording "O Allah, I have conveyed," in different contexts, some with weak chains of narration, and some whose narrators are trustworthy.