The Prophet ﷺ said, and he then mentioned the same meaning, but he did not mention "as long as he has not yet eaten food."He added that Qatada said, "This applies as long as the two have not yet been fed solid food. Once they have been fed, both are washed alike."
حدثنا ابن المثنى حدثنا معاذ بن هشام حدثني أبي عن قتادة عن أبي حرب بن أبي الأسود عن أبيه
أن النبي ﷺ قال فذكر معناه ولم يذكر ما لم يطعم زاد قال قتادة هذا ما لم يطعما الطعام فإذا طعما غسلا جميعا
[Sahih] Reported by Tirmidhi, Prayer, chapter on what has been mentioned regarding sprinkling water on the urine of a nursing infant boy, hadith 610, and Ibn Majah, hadith 525, from the hadith of Muaz bin Hisham, with this wording. Tirmidhi said, "Hasan," and Ibn Khuzayma graded it sahih, hadith 284, as did Ibn Hibban, hadith 247, and Hakim, 10/165, and Dhahabi agreed with him.