Hawzah News Agency – Imam al-Sadiq peace be upon him says:

إذا أحْسَنَ المُؤمنُ عمَلَهُ، ضاعَفَ اللَّهُ عَمَلَهُ لكُلِّ حَسَنةٍ سَبعَمائةٍ، وذلكَ قولُ اللَّهِ تباركَ وتعالى: (واللَّهُ يُضاعِفُ لِمَنْ يَشاءُ).

'When the believer excels in his good deed, Allah will enhance each one of his good deeds to equal seven hundred, for Allah, Blessed and most High, says: "Allah enhances severalfold whomever He wishes."

Source: Bihar al-Anwar, v. 71, p. 247, no. 7