Is it permissible to supplicate using "Kaf Ha Ya 'Ain Saad" and "Alif Lam Mim" and similar isolated letters, based on the understanding that they are oaths from Allah or from His Beautiful Names, as has been reported from some Companions?

There are no authentic chains of narration (asanid) confirming that the disconnected letters (al-ḥurūf al-muqaṭṭaʿah) at the beginning of the surahs are names of Allah. The Sahifah of Ali ibn Abi Talhah from Ibn Abbas is weak due to the weakness of its narrator and a discontinuity (inqita') between him and Ibn Abbas, as noted by Al-Albani and Al-Mu'allimi Al-Yamani. Similarly, the isnad of Al-Suddi from Ibn Abbas and Ibn Mas'ud is also weak. Al-Suddi mixed authentic narrations with unauthentic ones, as clarified by Ibn Taymiyyah and Ibn Hajar. Furthermore, the statement of some scholars that the disconnected letters are among the names of Allah is not supported by an authentic chain of narration and its meaning is not sound. This view has been rejected by a number of scholars, such as Al-Maturidi and Al-Tahir ibn Ashur. Therefore, it is not permissible to call upon Allah using them. The supplications mentioned in the Qur'an and Sunnah are sufficient for a Muslim.