Musannaf Ibn Abi Shayba 9:1161

Hafs narrated to us, from al-Shaybani, from al-Sha'bi, who said: Whatever is by way of *wujur* (pouring medicine into the side of the mouth) or *su'ut* (nasal drops) within the two years, it is breastfeeding. And whatever is after that, it is not breastfeeding.