In Syriac Christianity, the Fast of Nineveh is a three-day fast starting the third Monday before Clean Monday from Sunday Midnight to Wednesday noon, during which participants usually abstain from all dairy foods and meat products.

However, some observe the fast more rigorously and abstain from food and drink altogether from Sunday midnight to Wednesday after Holy Qurbana, which is celebrated before noon.

The three day fast of Nineveh commemorates the three days that Prophet Jonah spent inside the belly of the Great Fish and the subsequent fast and repentance of the Ninevites at the warning message of the prophet Jonah according to the bible.