Shaykh Abdul-Azeez Aal us-Shaykh on saying In Shaa Allaah when making Dua:
Is it wrong for me to say In Shaa Allaah (If Allaah Wills) when making Dua for someone else, for example I would say ‘Jazak’Allaah khairun In Shaa Allaah’ (May Allaah reward you if Allaah Wills)?
Answer: No, you cannot say this. Saying this is not permissible. The Messenger of Allaah (peace and blessings upon him) said, “Let no one say, ‘O Allaah forgive me if You Will, O Allaah have mercy upon me if You Will’ in an effort to resolve the matter because Allaah cannot be forced into doing anything.” And in another narration he said, “Verily, nothing that Allaah gives is a burden upon him.”
Translation Source: Masjid Tawheed Wa Sunnah of Durham, North Carolina: http://mtws.posterous.com/
Internet Source : http://ahlulsunnahwaljammah.wordpress.com