Sayyiduna Samurah bin Jundub (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "Every child is born upon the fitrah (natural disposition), but 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 / 11947