Yahya related to me from Malik from Zihad ibn Abi Ziyad the mawla
of Abdullah ibn Ayyash ibn Abi Rabia from Talha ibn Ubaydullah ibn
Kariyz that the Messenger of Allah, may Allah bless him and grant him
peace, said, "The most excellent dua is the dua on the Day of Arafa,
and the best of what I and the prophets before me have said, is 'There
is no god but Allah, alone, without partner.'"
Muwatta Malik Book 20, Hadith 258