Sayyidah Khawlah bint Qays bin Qahd (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) said: "Shall I not tell you of the things that expiate sins? Performing ablution (wudu) thoroughly despite difficulty, taking steps towards the prayers, and waiting for the next prayer after a prayer."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20963