أَرْبَعِينَ لَيْلَةً
Forty nights.
The period emphasizes the gravity of consulting a diviner. The hadith uses the words «لَمْ تُقْبَلْ لَهُ صَلَاةٌ», 'his prayer is not accepted'; a different legal ruling should not be substituted for the quoted wording.
Turning to the diviner in the hope of testing a prediction, or treating him as a trusted source, does not diminish the severity of this warning.