Is Jesus saying "God willing" the same as "Insallah", said by Muslims before doing anything? Is Jesus saying "God willing" the same as "Insallah" said by Muslims before doing anything?
Inshallah is simply the Arabic for 'God willing' or 'if God wills'. If any person of any religion were to say "God willing" in Arabic, they would say "Inshallah". The word 'Allah' just means 'God' in Arabic, and is used by Arabic Christians to refer to the Christian God. 'Inshallah' is used by Christians to express the concept of "If God wills" (which is found in James 4: 13-15, and is not spoken by Jesus). Although widely associated with Islam, it is not specifically an Islamic expression.

So the concept of things happening only 'if God wills' exist both in Christianity and Islam, and the same word is used for both in Arabic, which is 'Inshallah'. Deducing from that support by the New Testament writers for Islam (which post-dated the New Testament by hundreds of years) would be unwarranted.