Iddah of mukhtali'ah

Ibn Abbas narrated that:

The wife of Thabit bin Qais was granted a Khul from her husband during the time of the Prophet. So the Prophet ordered her to observe an Iddah of a menstruation.

[Jaami al-Tirmidhi Hadith No. 1185]

Abuu 'iisaa [al-Tirmidhi] said:

The scholars have differed in regards to the 'iddah of the mukhtali'ah. The majority of the Companions (may Allaah be pleased with them) of the Prophet (sallallaahu alayhi wa sallam) and others have said that the 'iddah of the mukhtali'ah is the same as the 'iddah of the divorced woman which is three periods. It is also the opinion of Sufyaan al-thaurii and the People of al-Kufah. 

Ahmad and IsHaaQ also held this opinion. 

A group of the Companions (sallallaahu alayhi wa sallam) of the Prophet (sallallaahu alayhi wa sallam) and others were of the opinion that the 'iddah of the mukhtali'ah is one period [i.e. one menstruation]. 

IsHaaQ said that if a person chooses this it is a strong Madhhab.