Is merely repenting and diligently performing prayers after a period of neglecting them for days sufficient for returning to Islam and having one's deeds accepted, or is a ghusl (ritual bath) or other conditions required, and is uttering the Two Testimonies enough?

Neglecting prayer out of laziness for several days is a grave sin, but is it an act of disbelief (kufr) or not? This is a matter of scholarly disagreement. The majority of scholars do not consider it disbelief, while others view it as disbelief upon abandoning even one prayer. Some, however, lean towards the view that it is only disbelief if one abandons it completely. If you have fallen into major disbelief, then as long as you have repented to Allah and returned to prayer, this is sufficient. There is no requirement for you to perform ghusl, utter the two testimonies of faith (shahadatayn), or shave your head for your Islam to be valid. Your prayer is considered a repentance through which you become a Muslim. As for what was narrated from the Prophet, peace and blessings be upon him, when he said to someone who embraced Islam, "Shave off the hair of disbelief," this is understood by the majority of scholars as a recommendation.