QURAN 9:36
Verily, the number of months with Allah is twelve months (in a year), so was it ordained by Allah on the Day when He created the heavens and the earth; of them four are Sacred, (i.e. the 1st, the 7th, the 11th and the 12th months of the Islamic calendar).

Bilal bin Yahya bin Talhah bin `Ubaidullah narrated from his father, from his grandfather Talhah bin `Ubaidullah that when the Prophet (ﷺ) would see a crescent moon, he would say:

TRANSLATION:
O Allah, bring it over us with blessing and faith, and security and Islam. My Lord and your Lord is Allah.

Usamah bin Zaid said:
"I said: 'O Messenger of Allah (ﷺ), I do not see you fasting any month as much as Shaban.'
He (ﷺ) said: 'That is a month to which people do not pay much attention, between Rajab and Ramdhaan. It is a month in which the deeds are taken up to the Lord of the worlds, and I like that my deeds be taken up when I am fasting."'

Narrated: Abu Salamah
"I asked Aishah about the fasting of the Messenger of Allah (ﷺ) and she said: '
He (ﷺ) used to fast until we would say: "He (ﷺ) has fasted," and he (ﷺ) used not to fast until we would say: "He (ﷺ) is not fasting." And I never saw him (ﷺ) fast more in any month than he fasted in Shabaan. He (ﷺ) used to fast all of Shabaan, he used to fast all of Shaaban but a little."

It was narrated from Abu Salamah that Umm Salamah said:
"I never saw the Messenger of Allah (ﷺ) fast two consecutive months, but he used to join Shabaan to Ramdhaan." '

PROPHET MUHAMMAD (ﷺ) said:
When a half of Shabaan remains then do not fast.

PROPHET MUHAMMAD (ﷺ) said:
When it is the middle of Shaaban, do not fast until Ramdhaan comes.

PROPHET MUHAMMAD (ﷺ) said:
None of you should fast a day or two before the month of Ramadan unless he has the habit of fasting (Nawafil) (and if his fasting coincides with that day) then he can fast that day.

It was narrated that Abu Salamah said:
“I heard ‘Aishah say: ‘I used to owe fasts from the month of Ramdhaan, and I would not make them up for until Shabaan came.’”

PROPHET MUHAMMAD (ﷺ) said:
Fasting three days of EACH MONTH is fasting for a lifetime, and the shining days of Al-Bid, the thirteenth, fourteenth and fifteenth.

Narrated: Abu Dhar
The Messenger of Allah (ﷺ) commanded us to fast the three days of Al-Bid, the thirteenth, fourteenth and fifteenth.

PROPHET MUHAMMAD (ﷺ) said:
If you want to fast at any time during the month then fast on the thirteenth, fourteenth and fifteenth.

Narrated: Abu Dhar
"The Messenger of Allah (ﷺ) said:
'Whoever fasts three days in every month, then that is (similar to) fasting every day (life time).' Then Allah Mighty and Sublime is He, attested to that in His Book, by revealing: (Quran 6:160) Whoever brings a good deed, shall have ten times the like thereof. So a day is like ten."

PROPHET MUHAMMAD (ﷺ) said:
EVERY NIGHT when it is the last third of the night, Our Lord (Allah), the Superior, the Blessed, descends to the nearest heaven and says:
1) Is there anyone to invoke Me that I may respond to his invocation?
2) Is there anyone to ask Me so that I may grant him his request?
3) Is there anyone asking My forgiveness so that I may forgive him?.

But no, by your Lord, they will not [truly] believe until they make you, [O Muhammad ﷺ], judge concerning that over which they dispute among themselves and then find within themselves no discomfort from what you (ﷺ) have judged and submit in [full, willing] submission.

Narrated 'Abdullah bin 'Amr:
Messenger of Allah (ﷺ) said:
"What befell the children of Isra'il will befall my Ummah, step by step, such that if there was one who had intercourse with his mother in the open, then there would be someone from my Ummah who would do that.
Indeed the children of Isra'il split into seventy-two sects, and my Ummah will split into seventy-three sects. All of them are in the Fire Except one sect."
He said: "And which is it O Messenger of Allah (ﷺ)?"
He (ﷺ) said: "What I am upon and my Companions."

PROPHET MUHAMMAD (ﷺ) said:
1) Indeed, whomever among you lives, he will see much differences.
2) Beware of the newly invented matters, for indeed they are astray.
3) Whoever among you sees that, then he must stick to my Sunnah and the Sunnah of the rightly guided Khulafa (Sahaaba),' cling to it with the molars.

PROPHET MUHAMMAD (ﷺ) said:
1) Whomsoever Allah guides, none can lead him astray,
2) And whomsoever Allah sends astray, none can guide.
3) The truest of word is the Book of Allah
4) And best of guidance is the guidance of Muhammad (ﷺ).
5) The worst of things are those that are newly invented;
6) Every newly-invented thing is an innovation
7) And every innovation is going astray,
8) And every going astray is in the Fire.

PROPHET MUHAMMAD (ﷺ) said:
If somebody innovates something which is not present in our religion, that thing is rejected.

PROPHET MUHAMMAD (ﷺ) said:
Whoever does something that is not in accordance with this matter of ours will have it rejected.

PROPHET MUHAMMAD (ﷺ) said:
I am your predecessor at Al-Hauh (Al- Kauthar), and some of you will be brought in front of me till I will see them and then they will be taken away from me and I will say, 'O Lord, my companions!' It will be said, 'You (ﷺ) do not know what they innovated (new things) in the religion after you left.

Narrated: Abdullah Bin Masud
PROPHET MUHAMMAD (ﷺ) said:
Among those in charge of you, after I am gone,
1) Will be men who extinguish the Sunnah and follow innovation.
2) They will delay the prayer from its proper time.”
I said: “O Messenger of Allah (ﷺ), if I live to see them, what should I do?”
He (ﷺ) said: “You ask me, O Ibn ‘Abdullah, what you should do? There is no obedience to one who disobeys Allah.”