(… while they are disbelievers in the Beneficent…) [13:30].
The commentators of the Qur’an said: “This verse was revealed at the treaty of Hudaybiyyah when they were about to write the document of the treaty. The Messenger of Allah, Allah bless him and give him peace, said to ‘Ali: ‘Write in the Name of Allah, the Beneficent (al-Rahman), the Merciful’. Sahl ibn ‘Amr and the idolaters said: ‘We do not know anyone by the name of the beneficent (al-Rahman) except the ruler of al-Yamamah’, meaning Musaylimah the liar, ‘rather, write: in Your Name, O Allah!’ This is how the people of the pre-Islamic period used to write. And so Allah, exalted is He, revealed about them this verse”.
Said ibn ‘Abbas, according to the report of al-Dahhak: “This was revealed about the unbelievers of Quraysh when the Prophet, Allah bless him and give him peace, said to them (… Adore the Beneficent! They say; And what is the Beneficent? Are we to adore whatever thou (Muhammad) biddest us?) [25:60], and so Allah, exalted is He, revealed this verse. He said (Say) to them, the Beneficent Whom you deny (He is my Lord; there is no god save Him…)”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou