Saying Inshaa Allaah in Du'aa

When Shaykh al-‘Uthaymeen was asked about the issue of saying inshaa Allaah in du’aa, he said:

It is not good for an individual to say, inshaa Allaah in his du’aa when he supplicates to Allaah; rather he should be firm and determined in his request, because no one can compel Allaah the exalted, and He said: "Call upon Me; I will respond to you.” [Soorah Ghaafir: 60]  So since He has promised to respond to the supplication, there is no need to say inshaa Allaah, because if Allaah guides a servant to du’aa, He will certainly respond to him either by giving him his request or repelling an evil from him or by preserving it for him on the Day of Resurrection.

It is established from the Prophet (sallallaahu alayhi wa sallam) that he said: “None of you should say: 'O Allah, forgive me if You wish; O Allah, be merciful to me if You wish,' but he should always appeal to Allaah with determination, for nobody can force Allaah to do something against His Will.” Recorded by al-Bukhaaree and Muslim

If a person were to ask, ‘Is it not confirmed from the Prophet (sallallaahu alayhi wa sallam) that he used to say to a sick person, “Do not worry, it will be a purification (for you), Allaah willing?” We will respond by saying, ‘Yes, but it is apparent that he didn’t say it as a form of du’aa; rather he said it as a form of notification and hope. It is not supplication, because one of its etiquettes is that the individual should be firm in it. And Allaah knows best.

Source: Fataawaa al-‘Aqeedah, p. 48-49, by Shaykh Muhammad Saalih al-‘Uthaymeen (may Allaah have mercy on him)