Is it true that in Imaam Tirmithi's collection of Hadeeth there is a Hadeeth to the following effect?
Hudhayfah narrates that they were with the Prophet (sallallaahu alayhi wa sallam) when he said: 'I do not know how long I will be with you for, so follow the command of these two after me (pointing to Abu Bakr and 'Umar), hold fast to the Covenant of 'Ammaar and whatever ibn Mas'ood narrates to you of my Hadeeth, believe.
If it exists in Tirmithi then I have the following questions:
# How authentic is it?
# Is the 'Ammaar mentioned the famous Ibn Yasaar?
# Is the ibn Mas'ood mentioned the famous Abdullaah?
# What is the Sharh of the Hadeeth?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The narration to which the questioner pointed is an authentic narration reported by At-Tirmithi in the chapter ‘the excellence of  'Ammaar Ibn Yaaser it is also reported by Imaam Ahmad but the wordings are At-Tirmithi’s. Huthayfah narrated that they were sitting with the Prophet who said: "I do not know for how long I will live amongst you, so follow those after me, and he pointed to Abu Bakr and ‘Umar and follow the guidance of ‘Ammaar, and whatever Ibn Mas’ood narrates to you, believe him."   At-Tirmithi said that this is a sound narration and Al-Albaani said that it is an authentic narration.

There is no doubt that 'Ammaar, who is mentioned in the narration is 'Ammaar Ibn Yaaser as At-Tirmithi entitled the narration on his name, and Ibn Mas’ood is 'Abdullaah Ibn Mas’ood .

The saying of the Prophet : "Follow the example of those after me…” is an order to follow the example of Abu Bakr and ‘Umar and his saying: “…and follow the guidance of ‘Ammaar,…"  means follow his path and methodology. Al-Mubaarak poori said: 'It seems that following the example is more general than following the guidance, as the example comprehends the words and actions, whereas the guidance includes only the actions.” His, saying ,: "Whatever Ibn Mas’ood narrates to you…'  means believe his sayings/words whether in regard to what he narrates from the Prophet or else. 

Allaah Knows best.