Can he pray Duha if he did not pray Fajr on time?

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If he prays ‘Isha’ with Maghrib at the time of Maghrib, he can pray Witr immediately after that.
Is Witr prayer different from the night prayer?

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Related Answers:
He wants to pray the obligatory prayers only and not the naafil prayers
Making up naafil acts of worship
There is no Sunnah prayer after the fard prayer of Fajr
If he prays ‘Isha’ with Maghrib at the time of Maghrib, he can pray Witr immediately after that.
Is Witr prayer different from the night prayer?

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