Ahmad Ibn Hanbal:
Muhammad bin Umar Al-Madini:
قد احتاط فيه اسنادا ومتنا ولم يورد فيه إلا ما صح عنده
"He (Ahmad bin Hanbal), was careful with the chain and the content, hence he only recorded what is authentic according to him."
Source: Khasa'is Musnad Ahmad. Pg. # 34 - 35.
Hanbal Ibn Ishaq said: 'Our uncle (Ahmad) gathered us, me, Saleh and Abdullah. He taught us "Al-Musnad" and nobody else heard it in its complete form except us. And he (i.e. Ahmad Ibn Hanbal) said: "This book is what I compiled and picked from more that seven hundred and fifty thousand Hadeeths, whenever the Muslims argue about a Hadeeth of the Messenger of Allah (saw) you should turn to this book, if you find it in this book then it is true, and if not then it is not true."
(Al-Albani says): 'This is what Al-Hafiz Al-Madini in "Al-Khasaes" and Ibn Al-Jawzi in "Manaqib Imam Ahmad" have narrated through two chains from Hanbal, so it is firm and Saheeh 'Authentic.'
Source: Al-Zaab Al-Ahmad. Pg. # 12.
It is also narrated by Ibn Majah and Al-Nisa'i in this form, and they also have narrated this Hadeeth through another chain through Muhammad ibn Amr ibn Ata from Salama ibn Al-Azraq from Abi Huraira and it’s narrators are 'Thiqh' Trustworthy.
Source: Fathul Bari Sharh Saheeh Al-Bukhari. Vol. 4, Pg. # 18 - 19.
Ibn Abi Shayba:
Explanation of Al-Sindi: In Al-Fath Al-Bari said: 'It’s narrators are 'Thiqh' (Trustworthy!)