[Some Narrations Regarding Intercession (Tawassul)]

Answer— and Allah is the Grantor of success: What has been narrated regarding the prophets’ seeking intercession by the Five—may Allah’s blessings be upon them—is sound; numerous narrations from the Prophet (May Allah bless him and his family and grant them peace) have come regarding it, especially the intercession of Adam. Ibn Taymiyyah, despite his strictness in this chapter, acknowledged its authenticity in some of his books. I heard this from my master, the Proof, Majd al-Dīn al-Mu’ayyidī—may Allah, Exalted is He, support him.
Yes, seeking intercession by the right of the Five, and by the rest of the Imams from the Household, and by all righteous servants of Allah, is legislated—contrary to what the ignorant claim, that it is a polytheistic innovation that places its doer among the idolaters. The scholars of the Muslims have answered the proponents of this view and cited what has come regarding intercession from the Prophet, (May Allah bless him and his family and grant them peace).
The legislated intercession is for the supplicant to say: O Allah, I ask You by the right of Muhammad and his family, or by the right of other righteous servants of Allah, or the like. As for expressions such as: I ask you, O ʿAlī, or O so-and-so, relieve me, or I seek refuge with you from Satan the accursed—these have not been transmitted in this wording and the like; rather, what is transmitted is as we have mentioned.
As for the ruling on this matter: it is not permissible to judge the one who says such words as a polytheist or an innovator. That is because seeking refuge and requesting aid from other than Allah, Exalted is He, is permissible.
The proof for this is His saying, Exalted is He: “And if they seek your help in the matter of religion, then upon you is help …” [Al-Anfāl:72]; and His saying, Exalted is He: “So the one who was from his faction sought his help against the one who was from his enemy …” [Al-Qaṣaṣ:15]; and His saying, Exalted is He, as a narrative: “If only I had against you some power, or could take refuge in a strong support.” [Hūd:80]. The Messenger of Allah (May Allah bless him and his family and grant them peace) sought protection, upon his return to Makkah, with al-Muṭʿim ibn ʿAdī, and he granted him protection. This is a matter well known in Islam and before Islam; the Messenger (May Allah bless him and his family and grant them peace) came with Islam and affirmed it, not rejecting it—rather, as we have mentioned, he (May Allah bless him and his family and grant them peace) sought protection from a polytheist, al-Muṭʿim ibn ʿAdī.
It is rationally and legally permissible for a person to seek refuge from his enemy by a mountain, a fortress, or the like. Based on this, it is not said of one who seeks aid, protection, or refuge from a living or a dead person that he is an innovator or a polytheist. At most, what one who seeks aid from the dead has done is to request what does not occur, or from one who lacks the ability; and requesting that from a living or a dead person is not shirk.
If it is said: Then what is shirk?
We say: Shirk is the worship of other than Allah, Exalted is He. What was mentioned previously is not worship; rather, it is a request and a supplication. It is not permissible to construe it otherwise with respect to Muslims.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3