Sayyidah Aishah Siddiqah (may Allah be pleased with her) narrates this saying of the Prophet (peace and blessings be upon him): "Whoever stands (in prayer) in Ramadan with faith and hoping for reward, his past sins are forgiven."
Al-Bazzar recorded it. Its chain contains a narrator, Ibrahim bin Isma'il bin Mujammi', and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5015