Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: When Sayyiduna Umar (may Allah be pleased with him) was wounded, I was the first to come to him. He said: Remember three things from me, for I fear that the people will not be able to reach me now: I have not given any ruling regarding kalalah, I have not appointed anyone as caliph over the people, and every slave of mine shall be counted free. Then the narrator mentioned the complete hadith.
Abu Ya'la recorded it in al-Kabir, and its narrators are thiqat (trustworthy). (It is stated this way in the Arabic text; perhaps the original wording should be:
Al-Tabarani recorded it in al-Mu'jam al-Kabir.)
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الوصايا / 7127