A very good friend of mine (works in Saudi) is due to get married in the month of October. We want the date to be fixed in the 1st week of October (in the last week of Rajab) but both his parents and girl's parents feel. They cannot fix the date till 6th of Sahabah). They feel a person cannot married before this date due to some assumption, belief, and no idea. I request that you let me know if there is restriction to getting married on any day in the Islamic calendar. Please quote authentic reference in order to convince to set the date in the first week of October. Please reply immediately as the marriage date is going to be fixed in couple of days. If the reply is received late. It will be too late if the date is fixed. Please rush your answer ASAP.May Allah bestow his blessing on Islam web and its member, for the noble cause undertaken by Islam web?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no harm in marrying at any time and any place except if there is any lawful reason, such as being in the state of Ihram or in Iddah (waiting period of a woman after divorce or death of her husband).
Therefore, the belief that marrying during certain period is not permissible, or observing an evil omen in a specific period are not-Islamic and belong to the pre-Islamic period.
Imam Nawawi , in his explanation of Sahih Muslim while explaining the Hadith of Ayisha (Radiya Allahu Anha) said: "Allah's Messenger (Sallallahu Alaihi wa Sallam) contracted marriage with me in Shawwal and took me to his house as a bride during Shawwal" , Imam Nawawi said: ' Ayisha (Radiya Allahu Anha) meant to reject the faith of pre-Islamic era'. He continued, 'the belief of some people in these days that marrying in Shawwal and starting a marital life in this month is dislikeable is null and void. There is no evidence for such beliefs and they are remnants of pre-Islamic faiths'.
Allah knows best.