we talked of it before over here

there is another place as well, where we find that umar did not trust a hadeeth narrated by a sahabi
he would rather ask for proofs

let us see this narration, rather should i say authentic narrations from umar as quoted by muslim

Abd Sa’id Khudri reported: We were in the company of Ubayy b. Ka’b that Abu Musa Ash’ari came there in a state of anger. He stood (before us) and said: I ask you to bear witness in the name of Allaah whether anyone amongst you heard Allaah’s Messenger (sallAllaahu alayhi wa sallam) as saying: Permission (for entering the house) should be sought three times and if permission is granted to you (then get in). otherwise go back. Ubayy b. Ka’b said: What is the iiiatter? He said: I sought permission yesterday from ‘Umar b. Khattab three times but he did not permit me, so I came back; then I went to him today and visited him and informed him that I had come to him yesterday and greeted him thrice, then came back, whereupon he said: Yes, we did hear you but be were at that time busy, but why did you not seek permission (further and you must have never gone back until you were permitted to do so). He said: I sought permission (in the manner) that I heard Allaah’s Messenger (sallAllaahu alayhi wa sallam) having said (in connection ‘With the seeking of permission for entering the house of a stranger). Thereupon he (Hadrat Umar) said: By Allaah, I shall torture your back and your stomach unless you bring one who may bear witness to what you state. ‘Ubayy b. Ka’b said: By Allaah, none should stand with you (to bear testimony) but the youngest amongst us. And he therefore, said to Abu Sa’id: Stand up. So I stood up until I came to Umar and said: I heard Allaah’s Messenger (sallAllaahu alayhi wa sallam) say this.

[sahih muslim, (The Book of Manners),CHAPTER: ASKING PERMISSION TO ENTER A HOUSE]
there are other chains for this narration as well, here is the online link