Istighathah is calling for help particularly when in hardship. Isti^anah is more inclusive and broader in its definition of calling for help.
Suratul-Baqarah, Ayah 45 means, “Seek assistance (wasta^inu) through patience and prayer.” The Messenger of Allah, sallallahu ^alayhi wa sallam, said, “The sun shall near the heads of people on Judgment Day and whilst in that state they will call upon Adam for help (istaghathu bi Adam)”. This hadith indicates clearly that it is acceptable to ask for the help of other than Allah, with the firm belief that Allah is the Creator of benefit and harm.
Asking Allah by the Prophet is deemed permissible by the consensus of the top scholars (mujtahids). Tawassul is seeking to gain benefit or to alleviate harm by mentioning a Prophet or a righteous Muslim, in honor of the mentioned, with the firm belief that Allah is the Creator of benefit and harm. In Suratul-Ma`idah, Ayah 35 means, “Seek the means of obedience to Allah.” In the hadith related and authenticated by At-Tabaraniyy, The Prophet taught the blind man to ask Allah by him. The blind man did so, and Allah returned his sight to him.