Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) relates that the Prophet (peace and blessings be upon him) said: "Every child is born upon the fitrah (natural disposition), and his parents make him a Jew or a Christian."
Al-Bazzar recorded it; its chain contains Abbad bin Mansur, who is da'if (weak), and it is reported from Yahya al-Qattan that he declared him trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب القدر / 11948