Shama-il Tirmidhi Chapter 050, Hadith Number 008 (356).

Khaalid bin 'Umayr Radiyallahu 'Anhu and Shaweesa Radiyallahu 'Anhu Reported that 'Umar Radiyallahu 'Anhu instructed 'Utbah bin "Anhu Ghazwaan Radiyallahu 'Anhu that he should go with his companions (who consisted of three hundred mujahideen) towards the 'Ajami lands. And said: When you reach the boundary of the 'Arabian country, set up camp there". (The reason was that 'Umar Radiyallahu 'Anhu received 10 reports that the 'Ajamis intended attacking the 'Arab lands. In other narrations Yazdajard had asked the 'Ajamis for aid. This was on their path. For this reason 'Umar Radiyallahu 'Anhu sent an army to set up a blockade and seal the way) The army left, and when they reached Marbad Basrah, they saw strange white stones. The people first began asking one another, 'what is this?' The people said it was Basrah. (Basrah in the original language means whitish stones. Subsequently this became the name of the town. As if they had answered that this was also a type of stone). After that they went forward (according to the instructions of 'Umar Radiyallahu 'Anhu) till they reached the small bridge (of the Dajlah). The people said, this is the place (that 'Umar Radiyallahu 'Anhu had chosen), and set up camp there. The narrator narrated the full incident (i.e. the coming of the army from Khuraasaan and the victory of 'Utbah Radiyallahu 'Anhu). (As the intention of Imaam Tirmidhi is to describe the hardships and poverty, which will be mentioned at the end of the narration, he has shortened this narration. 'Utbah Radiyallahu 'Anhu recited a khutbah after the victory, which is mentioned in the 'Arabic commentary. In this khutbah, he mentioned the temporary nature of this world, and that the hereafter is everlasting and eternal etc. After the hamd and thana, he said: "The world is going to come to an end, and it is turning its face and going away. Only so much of the world is left, as when water is used up from a dish, and in the end only a little drop is left in it. You are going towards such a world which is everlasting and which will never come to an end. Therefore it is necessary that you go to such a world with the best you can attain, because it has been shown to us that jahannam - which is the abode for those who disobey Allah is so deep that if a pebble is thrown into it from the upper portion, it will not reach the bottom after seventy years. This place will be packed with people. How important it is that we take heed at this place. We have also been shown that jannah-which is the abode for those who obey Allah is so vast that the width of its door from one side to the other is the distance of forty years. It will also be filled with people. Therefore adopt only such deeds that will save one from the first abode, and will gain for one entrance in the abode of Allah's Pleasure. After that he mentioned his past condition, "I had witnessed with Rasulullah Sallallahu 'Alayhi Wasallam this conditions that I am from among those seven people who were with Rasulullah Sallallahu 'Alayhi Wasallam. We had nothing with us besides the leaves of trees for eating. Our mouths became bruised by eating it. Incidentally I obtained a sheet, which I shared in half with Sa'd. (Even in this world of distress and difficulty, Allah Ta'aal, blessed them with this reward). There is none among the seven of us who has not been appointed an amir of some place. (Because this group endured many hardships and made many sacrifices before they were appointed amirs, therefore the treatment of their groups was of the best which will be known from the experiences of the Amirs after this) You will in the near future experience the trials of those who will come after this".

Apparently the reason for 'Utbah Radiyallahu 'Anhu mentioning his condition is to make known two things. The first is that the difficulties that are experienced and tolerated in the path of the deen, are also mostly rewarded in this world. For the difficulties that one will experience, In-sha-Allah one will reap the rewards. The second is that if one confronts anything from an amir which disturbs one, one should tolerate it, as this is a very great blessing, compared to the conditions one will face in the near future.