It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) used to kiss the head, and at that time he (peace be upon him) would be fasting.
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2241
Hadith Gradingحکم دارالسلام:صحيح من حديث عائشة انظر: 29291