What is the evidence behind ‘Certainty rules over doubt’?

Question

The maxim الْيَقِينُ لَا يَزُولُ بِالشَّكِّ ‘Certainty rules over doubt’ is used by many scholars. I want to know where this Maxim was derived from

Also is there an ijma for this Maxim?

Answer 1

The reasoning is that certainty is backed by evidence whereas doubt is not, rather doubt is just an assumption or suspicion that is lacking evidence. Acting on ideas that lack evidence usually just ends in fitnah (chaos).

That applies in many contexts.

• For example, the justice system has a concept of "innocent until proven guilty" which is based on that principle of certainty over doubt. A person can't be blamed as guilty based on our doubts; we need evidence to blame them. Imagine... if people were punished over mere doubts that others had about them, there would be lots of injustice and loss of innocent lives. So evidence is important.
• Another example, humans are forgetful and waswasa (whispers of Satan) is a tool of Satan. People would go crazy if they kept suspecting they missed a step in wudu or suspected their wudu broke or doubted that they might have missed to pray a rakah and kept re-doing wudu and re-doing prayer again and again. Islam is an easy religion and one of mercy; so it tells us to dismiss doubts and stick to what we are certain about.

Just a few of many examples. Hope this helps.

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Update: In response to your clarification on the question, it's derived from the Qur'an and Sunnah. Someone already pointed out Qur'an 10:36. Another clear example is from a hadith of the Prophet (ﷺ).

The Messenger of Allah (ﷺ) said: If any one of you has pain in his abdomen, but is doubtful whether or not anything has issued from him, be should not leave the mosque unless he hears a sound or perceives a smell. - Sahih Muslim 362.

Here we see the one who has a doubt (whether he passed wind) to not act unless he has proof i.e., hears the sound of wind passing or smells a resulting odor. Otherwise, he should stay in the mosque and resume with prayer.

Answer 2

In addition to what has already been cited by Medi1Saif and Muslimah يا رب العالمين ; the the following ahadith are also used:

فليطرح الشك وليبن على ما استيقن

Ignore what is uncertain and proceed on the basis of what is certain.

^{— Sahih Muslim}

دع ما يريبك إلى ما لا يريبك

Leave what makes you in doubt for what does not make you in doubt.

^{— Sunan an-Nasai}