A person forgetfully wore a [stitched] robe before shaving his head and after throwing Jamrat al-'Aqabah al-Kubra. He then shaved his head and made tawaf al-ifada followed by sa'y and full release from ihram. What must he to do?

It is established in the Shafi'i school of jurisprudence that it is not obligatory for a pilgrim to make a fidya (compensation) for committing out of forgetfulness or ignorance any of the prohibitions of ihram that are prohibited for reasons of self-indulgence. These include using perfume, engaging in sexual intercourse, wearing sewn garments and covering the face or head. The fidya is only obligatory upon a pilgrim who knowingly and deliberately does any of the above.
Based on this, a pilgrim in a state of ihram is not blameworthy if he puts on a robe after stoning Jamarat al-'Aqaba out of forgetfulness or ignorance; his hajj is valid and he is not obliged to slaughter in compensation.
And God Almighty knows best.