Musnad Abu Ya'la al-Mawsili 42:382

Zuhayr narrated to us, Yahya ibn Abi Bukayr narrated to us, Zuhayr ibn Muhammad narrated to us, from Abdullah ibn Muhammad ibn Aqil, from Sa’id ibn al-Musayyib, from Abu Sa’id al-Khudri, that he heard the Messenger of Allah (may Allah bless him and grant him peace) say: "Shall I not guide you to something by which Allah expiates sins and increases good deeds?" They said: "Yes, O Messenger of Allah." He said: "Performing wudu thoroughly despite difficulties, taking many steps to the mosques, and waiting for the prayer after the prayer. There is no man among you who leaves his house in a state of purity, then prays the congregational prayer with the Muslims, then sits in the mosque waiting for the next prayer, but the angel says: 'O Allah, forgive him; O Allah, have mercy on him.'" "When you stand for prayer, straighten your rows, stand close together, and fill the gaps, for I see you from behind my back. When your Imam says 'Allahu Akbar,' then say 'Allahu Akbar.' When he bows, then bow. When he says 'Sami’ Allahu liman hamidah,' then say 'Allahumma Rabbana laka al-hamd.'" "The best of the rows is the first, and the worst of them is the last. The best of the women’s rows is the last, and the worst of them is the first. O assembly of women, when the men prostrate, lower your gaze so that you do not see the private parts of the men due to the tightness of their lower garments."