It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The most merciful of my Ummah towards my Ummah is Abu Bakr (may Allah be pleased with him), and the sternest of them in the religion of Allah is Umar (may Allah be pleased with him)." Then he mentioned the others after that.
Bishr bin al-Mufaddal, Isma'il ibn Ulayyah and Muhammad bin Abi Adi narrated it from Khalid al-Hadhdha, from Abu Qilabah, from the Prophet (peace and blessings be upon him) as mursal, except for his statement about Abu Ubaydah, which they connected at its end, making it from Anas bin Malik from the Prophet (peace and blessings be upon him). All of these narrators are thiqat (trustworthy) and firmly reliable, and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12188