One of the greatest acts of worship is prayer, invoking the Divine Being for aid. Islam specifies that prayer should only be directed to God. He is deemed in total control of every man’s destiny and
able to grant his needs and remove distress.
Allah, the Exalted, says: ”And invoke not besides Allah any such that will neither profit you not harm you, but if (in case) you did so, you shall certainly be one of the Zalimun (polytheists and wrong-doers”
Qur’an 10:106
Allah, the Exalted, says: “ Blessed be He Who sent down the criterion (of right and wrong, i.e. this Qur’an) to His slave (Muhammad) that he may be a warner ‘Alamin’ (mankind and Jinn). He to Whom belongs the dominion of the heavens and the earth, and Who has begotten no son (children or offspring) and for Whom there is no partner in the dominion. He has created everything, and has measured it exactly according to its due measurements. Yet they have taken besides Him other alihah (gods) who created nothing but are themselves created, and possess no power (of causing) death, nor (of giving) life, nor of raising dead.”
Qur’an 25:1-3
Giving anyone else - angels, prophets, Jesus, Mary, idols or nature - portion of one’s worship, which is essentially due only to Allah, such as prayer, is called Shirk and is the most enormous of sins in Islam. Shirk is the only unforgivable sin if not repented from, and it denies the very purpose of creation.
Allah, the Exalted, says: "Verily! Allah forgives not (the sin of) setting up partners (in worship) with Him, but He forgives whom He wills sins other than that, and whoever sets up partners in worship with Allah, has indeed strayed far away."
Qur'an 4:116