A man came to the Prophet (ﷺ) and said: How do you fast, Messenger of Allah? The Messenger of Allah (ﷺ) became angry at what he said.
When Umar observed this (his anger), he said: We are satisfied with Allah as Lord, with Islam as religion, and with Muhammad as Prophet. We seek refuge in Allah from the anger of Allah, and from the anger of His Apostle. Umar continued to repeat these words till his anger cooled down. He then asked: Messenger of Allah, what is the position of one who observes a perpetual fast?
He replied: May he not fast or break his fast. Musaddad said in his version: He has neither fasted nor broken his fast. The narrator, Ghaylan, doubted the actual wordings.
He asked: What is the position of one who fasts two days and does not fast one day?
He said: Is anyone able to do that? He asked: What is the position of one who fasts every second day (i.e. fasts one day and does not fasts the next day)?
He (the Prophet) said: This is the fast that David observed.
He asked: Messenger of Allah, what is the position of one who fasts one day and breaks it for two days? He replied: I wish I were given the power to observe that. Then the Messenger of Allah (ﷺ) said: The observance of three days' fast every month and of one Ramadan to the other (i.e. the fast of Ramadan every year) is (equivalent to) a perpetual fast. I seek from Allah that fasting on the day of Arafah may atone for the sins of the preceding and the coming year, and I seek from Allah that fasting on the day of Ashura' may atone for the sins of the preceding year.
Sunan Abi Dawud Book 14, Hadith 113
The Prophet (ﷺ) used to teach us the Istikhara for each and every matter as he used to teach us the Suras
from the Holy Quran. (He used to say), "If anyone of you intends to do something, he should offer a
two-rak`at prayer other than the obligatory prayer, and then say: 'Allahumma inni astakhiruka
bi'ilmika, wa astaqdiruka biqudratika, wa as'aluka min fadlika-l-'azim, fa innaka taqdiru wala aqdiru,
wa ta'lamu wala a'lamu, wa anta'allamu-l-ghuyub. Allahumma in kunta ta'lamu anna hadha-lamra
khairun li fi dini wa ma'ashi wa 'aqibati `Amri (or said, fi 'ajili `Amri wa ajilihi) fa-qdurhu li, Wa in
kunta ta'lamu anna ha-dha-l-amra sharrun li fi dini wa ma'ashi wa 'aqibati `Amri (or said, fi ajili `Amri
wa ajilihi) fasrifhu 'anni was-rifni 'anhu wa aqdur li alkhaira haithu kana, thumma Raddani bihi," Then
he should mention his matter (need).
Sahih al-Bukhari Book 80, Hadith 77
from the nephew of 'Abdullah bin Salam who said: "When they were about to kill 'Uthman, 'Abdullah bin Salam came and 'Uthman said to him: 'What did you come for?' He said: 'I came to assist you.' He said: 'Go to the people to repel their advances against me. For verily your going is better to me than your entering here.' So 'Abdullah went to the people and said: 'O you people! During Jahiliyyah I was named so-and-so, then the Messenger of Allah (ﷺ) named me 'Abdullah, and some Ayat from the Book of Allah were revealed about me. (The following) was revealed about me: "A witness from among the Children of Isra'il has testified to something similar and believed while you rejected. Verily, Allah does not guide the wrongdoing people. (46:10)" "Sufficient as a witness between me and you is Allah, and those too who have knowledge of the Scripture. (13:43)" Allah has sheathed the sword from you and the angels are your neighbors in this city of yours, the one in which the Revelation came to the Messenger of Allah (ﷺ). But by Allah! (Fear) Allah regarding this man; if you kill him, then by Allah! If you kill him, then you will cause the angels to remove your goodness from you, and to raise Allah's sheathed sword against you, such that it will never be sheathed again until the Day of Resurrection.'" He said: "They said: 'Kill the Jew and kill 'Uthman.'"
Jami` at-Tirmidhi Book 49, Hadith 203