Al-Matalib al-'Aliyah 572 — Completing the obligatory

It is narrated from Sayyiduna Yusuf bin Abdullah: I came to Sayyiduna Abu al-Darda' (may Allah be pleased with him) during the illness in which he died, and he asked me: "O my nephew, what has brought you to this land, and what purpose has put you to the hardship of coming here?" I said: "Nothing brought me here except the long-standing bond between you and my honoured father and the desire to maintain ties." At this Sayyiduna Abu al-Darda' (may Allah be pleased with him) said (emphasising the truth of his words): "This is a very evil hour for lying (that is, in this state of dying I will speak nothing but the truth). I heard the Messenger of Allah (peace and blessings be upon him) say: 'Whoever performs ablution (in the best manner), then stands and prays two or four rak'ahs, whether obligatory or voluntary, completing the bowing and prostration in them (with all their etiquettes and conditions), then seeks forgiveness and pardon from Allah Almighty, Allah will certainly forgive him.'"
Imam Ahmad recorded this hadith in his Musnad. Although there is criticism of the narrator Abu al-Mu'alla al-Tufawi in its chain, other sahih (authentic) hadith about the forgiveness of sins through ablution and prayer support it.