Huzaifa bin Yaman reported,
Umar was called to attend a funeral, so he set out for it, intending to join. I caught hold of him and said, "Sit down, Commander of the Believers, for he is one of those people."Umar said, "I adjure you by Allah, am I one of them?"He replied, "No. But I will not vouch for anyone after you."
Azami 9889
Sahihعن حذيفة بن اليمان قال
دعي عمر لجنازة، فخرج فيها أو يريدها، فتعلقت به فقلت: اجلس يا أمير المؤمنين، فإنه من أولئك، فقال: نشدتك بالله أنا منهم؟ قال: لا. ولا أبرئ أحدا بعدك.
No references are available.
Bazzar (2885) narrated it from Abdul-Wahid bin Ghiyath, who said, "Abdul-Aziz bin Muslim (that is, Qasmali) told us, Amash told us, from Abu Waail, from Huzaifa," and he mentioned it. Its chain of transmission is sahih, and Ibn Hajar also graded it sahih in Mukhtasar Zawaid Bazzar (590).This hadith contains a clear merit for Umar bin Khattab 
, namely his innocence from hypocrisy, because the Prophet ﷺ had disclosed the names of the hypocrites to Huzaifa bin Yaman and instructed him not to reveal them. This is why Huzaifa was given the title "keeper of the secret of the Messenger of Allah" ﷺ. His statement, "for he is one of them," refers to the hypocrites.