Three forms of tawassul are established by evidence: by Allah's names and attributes ("The most beautiful names belong to Allah, so call on Him by them" — Quran 7:180); by one's own righteous deeds (the ḥadīth of the three men trapped in the cave, who each asked Allah by a sincere deed — Sahih al-Bukhari 2215, from Ibn ʿUmar, and also in Ṣaḥīḥ Muslim); and by asking a living righteous person to supplicate for you, as ʿUmar did with al-ʿAbbās ibn ʿAbd al-Muṭṭalib when seeking rain (Sahih al-Bukhari 1010). What is not permitted is directing the dua itself to the dead or absent — asking a prophet or walī for help, rescue or forgiveness — because Allah says, "The places of worship are for Allah alone, so do not invoke anyone along with Allah" (Quran 72:18) and "Call upon Me; I will respond to you" (Quran 40:60). Tawassul by the mere status or "right" of a created being ("O Allah, by the right of Your Prophet") is a point of genuine ikhtilāf: many verifying scholars within the madhāhib, and the scholars of the Salafī manhaj, disallow it as having no authentic proof, while some other scholars permitted it. The principle to hold firmly is that no created being is ever called upon or asked for what only Allah can give; and rulings of shirk upon specific individuals are left to qualified scholars, after the conditions are met and the doubts removed.
Q&A · Dua & Dhikr
Is tawassul — seeking nearness to Allah through the Prophet or the righteous — permissible in dua?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.