The hadeeth, “Whoever neglects prayer, Allah will send fifteen punishments upon him, six in this world, three when he is dying, three in the grave and three when he emerges from the grave…” is a fabricated (mawdoo’) hadeeth which is falsely attributed to the Messenger of Allah (peace and blessings of Allah be upon him).
The six punishments in this life:
1. Allah takes away blessings from his age (makes his life misfortunate)
2.Allah does not accept his plea (du'a)
3.Allah erases the features of good people from his face.
4.He will be detested by all creatures on earth.
5.Allah does not reward him for his good deeds (no thawab)
6.He will not be included in the du'a (supplications) of good people.
The three punishments while dying:
1. He dies humiliated.
2. He dies hungry.
3. He dies thirsty. Even if he drinks the water of all the seas he will still be thirsty
The three punishments in the grave:
1. Allah tightens his grave until his chest ribs come over each other.
2. Allah pours on him fire with embers.
3. Allah sets on him a snake called "the brave", "the bold" which hits him from morning until afternoon for leaving the Fajr (early morning) prayer, from the afternoon until Asr (late afternoon) for leaving the Dhuhr (noon) prayer and so on. With each strike he sinks 70 yards under the ground
The three punishments on the day of judgement:
1. Allah sends who would accompany him to hell pulling him on the face.
2. Allah gives him an angry look that makes the flesh of his face fall down.
3. Allah judges him strictly and orders him to be thrown in hell.
Source: Islamqa.info