What is the maximum and the minimum limits of Mahr (mandatory gift to a bride from her groom)? Is it Haram (prohibited) to increase it?
There is no evidence in the Qur'an or the Sunnah on the recommended amount of Mahr. Some of the evidence mentioned in the Qur'an allow the payment of a large Mahr, while others are general and include both large and small. The first type includes Allah's saying (Exalted be He),
But if you intend to replace a wife by another and you have given one of them a Qintâr (of gold i.e. a great amount as Mahr) take not the least bit of it back
The (Part No. 19; Page No. 30) other type include Allah's saying (Exalted be He),
Also (forbidden are) women already married, except those (slaves) whom your right hands possess. Thus has Allâh ordained for you. All others are lawful, provided you seek (them in marriage) with Mahr (bridal-money given by the husband to his wife at the time of marriage) from your property, desiring chastity, not committing illegal sexual intercourse, so with those of whom you have enjoyed sexual relations, give them their Mahr as prescribed; but if after a Mahr is prescribed, you agree mutually (to give more), there is no sin on you. Surely, Allâh is Ever All-Knowing, All-Wise.
And Allah's Saying:
Made lawful to you this day are At-Tayyibât [all kinds of Halâl (lawful) foods, which Allâh has made lawful (meat of slaughtered eatable animals, milk products, fats, vegetables and fruits)]. The food (slaughtered cattle, eatable animals) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time when you have given their due Mahr (bridal-money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girl-friends.
The word "Mahr" is general and applies to both large and small sums of money. As for the evidence that is mentioned in the Sunnah, there are different situations in which there was great discrepancy in the Mahr, such as the Mahr of the Prophet's wives and daughters (may Allah be pleased with them), and the Mahr of the Sahabah's (Companions of the Prophet) wives (may Allah be pleased with them). Some of them were married by what the man had memorized of the Qur'an, (Part No. 19; Page No. 31) a pair of shoes, the weight of a stone of gold, or four Uqiyyahs (1 Uqiyyah = 40 Dirhams of silver = 119 grams). If you want to read more, you can refer to the two Sahih (authentic) Books of Hadith, the four Sunan (Hadith compilations classified by jurisprudential themes) and others. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.