The Muslim Personal Law (Shariat) Application Act of 1937 apparently sets no lower limit on marriage for Muslims. The Prohibition of Child Marriage Act 2006 then defined a child as a female under 18 and a male under 21, and a child marriage is one where at least one party is a child. The law then says that "Every child marriage is voidable at the option of the contracting party who was child at the time of solemnization of marriage". The punishment (not at the discretion of the child) for a male offender is rigorous "imprisonment which may extend to two years" or a fine of 100,000 rupees (or both). While the political question of modifying the law to allow Sharia and Nikah to prevail for Muslims, the current law does not allow this.
The crime is a cognizable offense (section 15), meaning that no court order is required for police to arrest without warrant, and bail is not available.