It is narrated from Sayyiduna al-Miqdam bin Ma'di Karib (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, Allah enjoins you regarding your mothers; indeed, Allah enjoins you regarding your mothers; indeed, Allah enjoins you regarding your fathers; indeed, Allah enjoins you regarding your closest relatives, then the next closest."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17773