Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: This verse was revealed concerning the Bedouins: "Whoever brings a good deed will have ten times its like." A man said: "O Abu Abd al-Rahman, what reward will the Muhajirun receive?" Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: "Something more excellent than that (which is mentioned in this verse): 'Indeed, Allah does not wrong even the weight of an atom; and if it is a good deed, He multiplies it and gives from Himself a great reward.'"
Imam al-Tabarani recorded it. Its chain contains a narrator, Atiyyah, who is da'if (weak). A hadith about good deeds being multiplied up to two million times will come in the Book of Repentance and the Book of Remembrances, if Allah wills.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11010