Sayyiduna Anas (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him), while in the state of ihram, got cupped on the top of his foot.
In the narrations of Ibn Buhaynah and Ibn Abbas it is on his head, and a number (of narrators) are more likely to have preserved it than one, unless he (peace and blessings be upon him) did it twice while in ihram; and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19530