Completing the obligatory from the voluntary, and chapter: Unrestricted voluntary prayers

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever performs twelve rak'ahs (sunnah or voluntary) in a day, Allah Almighty will make his flesh forbidden to the Fire of Hell." (Sayyiduna Anas (may Allah be pleased with him)) said: "So I have never abandoned these twelve rak'ahs since then."
[Takhrij: Musnad Abi Ya'la: 571, Majma' al-Zawa'id: 2/220; according to Allamah al-Haythami, the narrators of its chain are thiqat (trustworthy).]

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.

It is narrated from a servant (man or woman) of the Messenger of Allah (peace and blessings be upon him) that the Prophet (peace and blessings be upon him) used to (often) ask him: "Do you have any need?" Until one day he said: "O Messenger of Allah, I have a need." He (peace and blessings be upon him) asked: "What is your need?" He said: "My need is that you intercede for me on the Day of Resurrection (that is, become the means of my forgiveness)." He (peace and blessings be upon him) asked (expressing wonder and joy): "Who guided you to this (lofty aim)?!" He replied: "My Lord (put this into my heart)." He (peace and blessings be upon him) said: "Then help me (in attaining this wish of yours and in your becoming deserving of my intercession) through abundant prostration (that is, by praying abundantly)."
Imam Ahmad recorded this hadith in his Musnad, and Allamah al-Albani along with other hadith scholars declared its chain hasan (good) or sahih (authentic).

It is narrated from Sayyiduna Suhayb (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A man's performing a voluntary prayer in a place (in seclusion and solitude) where people do not see him carries twenty-five times more merit and reward than his praying (openly) in the presence of people."
Imam Abu Ya'la recorded this hadith in his Musnad, and Allamah al-Haythami declared its narrators thiqat (trustworthy) in Majma' al-Zawa'id.

It is narrated from the Mother of the Believers, Sayyidah Maymunah (may Allah be pleased with her), that the Messenger of Allah (peace and blessings be upon him) said: "Allah, the Blessed and Exalted, says: 'Whoever harms one of My awliya' (chosen servants) has become deserving of My declaration of war. Of the deeds by which My servant draws near to Me, the most beloved to Me are the obligations that I have made binding upon him; and My servant continues to draw near to Me through voluntary acts of worship until I love him. Then, when I love him, I become his foot with which he walks, his hand with which he grasps, his tongue with which he speaks, and his heart with which he understands. If he asks Me for something, I will surely give it to him, and if he calls upon Me, I will surely answer his call. And I have never hesitated in doing anything as I hesitate at the death of My servant, because he dislikes death and I dislike causing him distress.'"
This narration is da'if (weak).
I (Ibn Hajar) say: On this topic there are also hadith narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) in Imam al-Bukhari's collection, and from Sayyidah Aishah and Sayyiduna Anas (may Allah be pleased with them both).