As in the field of asbab al-nuzul, the information about al-nasikh wa al-mansukh cannot be accepted upon mere personal opinion, guesswork or hearsay, but must be based on reliable reports, according to the ulum al-hadith, and should go back to the Prophet and his Companions.

The report must also clearly state which part of the revelation is nasikh and which is mansukh.

Some scholars say that there are three ways of knowing about al-nasikh wa al-mansukh:

• Report from the Prophet or Companions.

• Ijma' (consensus of the umma upon what is nasikh and what mansukh).

• Knowledge about which part of the Qur'an preceded another part in the history of revelation. [Qattan, op.cit., p. 199]

Example:

Narrated Mujahid (regarding the verse):

Those of you who die and leave wives behind, they (their wives) shall await (as regards their marriage) for four months and ten days (2: 234).

The widow, according to this verse, was to spend this period of waiting with her husband's family, so Allah revealed: Those of you who die and leave wives (i.e. widows) should bequeath for their wives, a year's maintenance and residence without turning them out, but if they leave (their residence) there is no blame on you for what they do with themselves, provided it is honourable (i.e. Lawful marriage) (2: 240).

So Allah entitled the widow to be bequeathed extra maintenance for seven months and 20 nights and that is the completion of one year. If she wished, she could stay (in her husband's home) according to the will, and she could leave it if she wished, as Allah says: Without turning them out, but if they leave (the residence) there is no blame on you.

So the idea (i.e. four months and ten days) is obligatory for her.

'Ata' said: Ibn 'Abbas said: This verse i.e. the statement of Allah ... without turning one out ... cancelled the obligation of staying for the waiting period in her late husband's house, and she can complete this period wherever she likes.

'Ata' said: If she wished, she could complete her 'idda by staying in her late husband's residence according to the will or leave it according to Allah's statement:

'There is no blame on you for what they do with themselves.'

'Ata' added: Later the regulations of inheritance came and abrogated the order of the dwelling of the widow (in her dead husband's house) so she could complete the 'idda wherever she likes. And it was no longer necessary to provide her with a residence.

Ibn Abbas said: This verse abrogated her (i.e. the widow's) dwelling in her dead husband's house and she could complete the 'idda (i.e. four months and ten days) (wherever she liked, as Allah's statement says: ...'without turning them out ...' [Bukhari, VI, No. 54.]