Is it permissible for a Muslim, while making Du`a' (supplication) to Allah, to say: "O servants of Allah's Most Beautiful Names, answer and fulfill my needs."?
Calling the servants of Allah's Most Beautiful Names to fulfill one's needs is Shirk (associating others with Allah in His Divinity or worship), for it involves calling imaginary servants beside Allah; a matter for which we know no evidence; Allah (Exalted be He) says:
And who is more astray than one who calls on (invokes) besides Allâh, such as will not answer him till the Day of Resurrection, and who are (even) unaware of their calls (invocations) to them?
And when mankind are gathered (on the Day of Resurrection), they (false deities) will become their enemies and will deny their worshipping.
Also Allah (Exalted be He) says:
And whoever invokes (or worships), besides Allâh, any other ilâh (god), of whom he has no proof; then his reckoning is only with his Lord. Surely! Al-Kâfirûn (the disbelievers in Allâh and in the Oneness of Allâh, polytheists, pagans, idolaters) will not be successful.
(Part No. 1; Page No. 134) Also Allah (Exalted be He) says:
"And invoke not besides Allâh, any such that will neither profit you nor harm you, but if (in case) you did so, you shall certainly be one of the Zâlimûn (polytheists and wrong-doers)."
And if Allâh touches you with harm, there is none who can remove it but He
Allah (Glorified and Exalted be He) says:
And the mosques are for Allâh (Alone): so invoke not anyone along with Allâh.
Allah (Exalted be He) says:
‘And verily, there were men among mankind who took shelter with the males among the jinn, but they (jinn) increased them (mankind) in sin and transgression.
Similarly, it is authentically reported that the Prophet (peace be upon him) said:
If you beg, beg of Allah Alone; and if you need assistance, beseech Allah Alone for help ...
There are other Ayahs (Qur'anic verses) and Hadiths that prove that Du`a' to bring good or ward off harm must be offered to Allah Alone. Hence, offering it to anyone other than Allah is Shirk because Du`a' is an act of `Ibadah (worship).