It is narrated from Sayyidah Khawlah bint Qays bin Qahd (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: "Shall I not inform you of the expiations for sins?" The people said: "Certainly, O Messenger of Allah." He (peace and blessings be upon him) said: "Performing ablution (wudu) thoroughly despite difficulty, taking many steps towards the mosques, and waiting for the next prayer after a prayer."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20964