Is it permissible to seek intercession (tawassul) or pray for rain (istisqa') through a deceased person, as the people of Samarkand did when they sought intercession through Imam Al-Bukhari at his grave for rain?

Seeking out prayers at the graves of the righteous and seeking blessings there is an error and contrary to the Sunnah (definition) and the guidance of the Salaf. Ibn Taymiyyah stated that the intention of visiting the graves of the righteous for prayer, supplication, seeking needs from them or from Allah at their graves, seeking their aid, or swearing by them to Allah, is an innovation that was not practiced by the Salaf, nor was it legislated by the Messenger of Allah, peace and blessings be upon him, and the great Imams of the Muslims prohibited it.