What is the correct time to begin fasting in Germany, taking into account the time of Fajr prayer (3:51) and sunrise (4:55), and the possibility of distinguishing a white thread from a black one before the aforementioned sunrise?

The time for abstaining from food and drink during fasting is from the appearance of true dawn (the Adhan for Fajr) until sunset, and not from sunrise. This is based on the Almighty's saying: "And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the night" (Al-Baqarah: 187). The Prophet, peace and blessings be upon him, interpreted the white and black threads as the whiteness of day and the blackness of night. If you are unable to determine the time of true dawn, then follow the word of someone you trust or rely on credible calendars, such as the Umm Al-Qura calendar.