Is it permissible to say, "For God's sake, my Lord [Ya Rabb]?"

It is commendable in supplication to show humility and submissiveness to Allah the Almighty, and to manifest one's need for Him. This is indicated by the texts of the Quran and Sunnah, and the actions of the Salaf (pious predecessors), as in the words of Allah the Almighty: ﴿Call upon your Lord humbly and privately﴾, and His saying: ﴿They call upon their Lord in fear and hope﴾. Ibn Abbas also described the state of the Prophet, peace and blessings be upon him, during the prayer for rain as "humble, meek, submissive, and lowly."

As for the supplicant's saying, "O Allah, I ask You by Allah, the One, the Unique, the Self-Sufficient…", this is a form of tawassul (seeking nearness to Allah through an intermediary), and it carries two possible interpretations: 1. Tawassul through the servant's faith and righteous deeds, meaning: I ask You, seeking nearness through my testimony that You are Allah, the One. 2. Tawassul through Allah's Most Beautiful Names and Exalted Attributes, meaning: I ask You, seeking nearness through what You have described and named Yourself with.

Regarding swearing an oath upon Allah in supplication, such as "By Allah, this will not happen," it is permissible and lawful if the motivation behind it is strong trust in Allah and good expectations of Him, while the servant acknowledges his weakness and does not impose anything upon Allah. This is similar to the hadith of Anas ibn an-Nadr: "Indeed, among the servants of Allah are those who, if they were to swear an oath upon Allah, He would fulfill it for them." However, if the motivation is arrogance and self-admiration, then it is forbidden and invalidates deeds, like a man saying: "By Allah, Allah will not forgive so-and-so."

Therefore, safety lies in adhering to a state of need and humility before Allah the Almighty in supplication, as this is most befitting for the servant's condition, just as the Master of Messengers, peace and blessings be upon him, did.