All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
First of all, you should know that the Maaliki view, which is also the chosen view of Shaykul-Islam Ibn Taymiyyah is that the ablution of the person who suffers from incontinence (continuous uncontrolled passing of wind, urine, etc.) is not invalidated by his discharge of impurity. He is not required to perform ablution except when his ablution is invalidated with his own choice (not because of his condition). Please, refer to fatwa 330445. Based on this scholarly view, the matter is quite clear: the person who suffers from incontinence should perform ablution for the Fajr prayer, for example, and if he retained his ablution until Thuhr, it is permissible for him to pray the Dhuha and the Thuhr with the same ablution (that of the Fajr).
That was the view of the Maaliki scholars. As for the view of the majority of the scholars, they held that the person who suffers from incontinence is required to perform ablution for each obligatory prayer. They held different views as to whether his ablution is invalidated by the end or the beginning of the prayer time, and both views are valid in the Hanbali school (according the view that ablution is invalidated by the end of the prayer time, his ablution is invalidated by the rise of the sun, but according to the view that ablution is invalidated by the beginning of the prayer time, his ablution is invalidation by the beginning of the Thuhr prayer).
Shaykh Ibn ‘Uthaymeen believed that the most likely correct view in this regard is that the person who suffers from incontinence should perform a separate ablution for the Dhuha prayer because it has a specific time interval within which it is to be performed. He was asked, “Is it permissible for that woman to pray the Dhuha with the ablution that she performed for the Fajr?”
He replied, “It is not permissible because the Dhuha prayer has a certain time frame, so it is essential to perform ablution for it after its time begins. This woman is like one who suffers from Istihaadhah (non-menstrual vaginal bleeding), and the Prophet, sallallahu ‘alayhi wa sallam, commanded the woman who suffered from Istihaadhah to perform ablution for each prayer.” There is no doubt that this is the more prudent thing to do in order to be on the safe side in terms of clearing oneself of their liability. The lay-Muslim is required to follow the opinions of a reliable scholar whose knowledge and righteousness he trusts.
The scholars who held that it is allowed for the person who suffers from incontinence to combine two prayers (Thuhr and ‘Asr together, and Maghrib and ‘Ishaa' together) are the Hanbalis, but the conditions required for combining the prayers according to the Hanbali view must be fulfilled in this case, one of which is performing the two combined prayers right after each other. We could not find any statement of the Hanbali scholars on whether the ablution of a person with incontinence who performs Thuhr and 'Asr at the time of the Thuhr is invalidated by the end of the time of the Thuhr prayer or not. As for the scholars who held that it is not allowed for him to combine the prayers, such as the Shaafi‘is and Hanafis, their view in this regard is clear.
Allah knows best.