From Sahih Bukhari (Hadith 5019):
Narrated `Abdul `Aziz bin Rufai':Shaddad bin Ma'qil and I entered upon Ibn `Abbas. Shaddad bin Ma'qil asked him, "Did the Prophet (ﷺ) leave anything (besides the Qur'an)?" He replied. "He did not leave anything except what is Between the two bindings (of the Qur'an)." Then we visited Muhammad bin Al-Hanafiyya and asked him (the same question). He replied, "The Prophet (ﷺ) did not leave except what is between the bindings (of the Qur'an)
Reference: Bukhari 5019