Iran was providing support for one or two of Afghan Shi'a Mujaheddin groups (and accepted about a million of refugees) during the Soviet War in Afghanistan of the 1980s-1988. Groups in qeustion were primarily active in Mazar-i-Sharif area. But, I do not know about Iran 'officially' providing sanctuaries to any of groups in question.

That said, the country (Iran) was in a state of chaos when the Soviets invaded, and then preoccupied with the Iran-Iraq War for the rest of the 1980s. By 1988, general condition of the Iranian military and security apparatus was so bad, the border to Afghanistan was barely controlled (or if, then only by day; by night it was various Iranian and Afghan drug-smuggling gangs that ruled).

Finding any kind of sources of reference in English language is likely to be rather problematic: online reporting about developments in Afghanistan used to be quite vivid back in the late 1990s, but most of websites in question disappeared long ago. Even the Iranian authorities ceased publishing details about security operations along the border to Afghanistan as of 2001 (although some of these were quite big, and included air strikes by the Iranian air force).

Various books published in the 1980s and 1990s are mentioning only bits and pieces. Online archives of the UNHCR are likely to have at least reports about Afghan refugees in Iran, which in turn might offer some useful clues.