Is it true that the Messenger (peace and blessings of Allah be upon him) used to have intercourse with his wives on Mondays and Thursdays, and is it obligatory to do so in adherence to his Sunnah?

Intercourse on Friday and its eve is considered desirable by a group of scholars, their evidence being a weak hadith narrated by Ibn Umar. Al-Hafiz Ibn Hajar mentioned that for one to perform ghusl (ritual bath) for janabah (state of ritual impurity) on Friday indicates the desirability of intercourse on Friday, so that a man's mind may be at peace from thinking about women, and to prompt the woman to perform ghusl. It has also been reported from Imam Ahmad and some of the Tabi'in (successors) that this is desirable, and Al-Qurtubi mentioned it as the most appropriate of sayings. As for intercourse on Mondays and Thursdays, there is no sound basis for it from the Prophet, peace and blessings be upon him.