There are a number of evidences from the Hadith of the Prophet (pbuh) which prove that not all Bidah are bad.
It is related in Bukhari and Muslim from Abu Hurayra that at the dawn prayer the Prophet (pbuh) said to Bilal, ‘Tell me which of your acts in Islam you are most hopeful about, for I have heard your footsteps in Paradise?’ and Bilal replied ‘I have done nothing I am more hopeful about than the fact that I do not perform wudu at any time without praying with that wudu whatever has been destined for me to pray.
Bukhari and Muslim relate Rifa’a ibn Rafi said ‘We were praying behind the Prophet (pbuh) and he raised from bowing and said ‘Allah hears whoever praises Him’ a man behind him said ‘Our Lord, Yours is the praise, abundantly, wholesomely and blessedly therein’
When the man was about to leave, the Prophet (pbuh) asked who said it, and when the man replied it was he, the Prophet (pbuh) said, ‘I saw thirty-odd angles each striving to be the one to write it.’
Bukhari relates from Aisha that the Prophet (pbuh) dispatched a man at the head of a military expedition who recited the Quran for his companions and finished each recital with Surah al-Ikhlas. When they returned, they mentioned this to the Prophet (pbuh) who told them to ask him why he does this. When they asked him, his reply was ‘Because it describes the All –Merciful and I love to recite it.’ The prophet (pbuh) said to them ‘Tell him, Allah loves him.’
Bukhari relates from Abu Sa’id al Khudri that a group of sahaba where on a journey when they asked some desert Arabs to be their host but they refuse.
The leader of these Arabs was then stung by a scorpion and his followers tried everything to cure him but were unsuccessful. They then asked the group of sahaba who said they would help but would charge a fee as when they asked the desert Arabs to host them, they refused.
A herd of sheep was agreed upon as the fee and a sahabi began spitting and reciting the Fatiha over the victim until he got up and began to walk as if nothing had happened to him. Before dividing up the sheep amongst the sahaba, they decided to ask the Prophet (pbuh).
The Prophet (pbuh) said to them ‘How did you know it was of the words which heal? You were right. Divide up the heard and give me a share.’