Your assumption is false, Muslims in India is increasing in an ever increasing rate. Bangladesh will always support the trend.
http://indianexpress.com/article/opinion/columns/myth-of-muslim-growth/
First, the total population growth rate declined from 21.5 per cent to 17.7 per cent, which is a continuation of the decline of the population of all religions since 1981. The decline has been somewhat faster than what many experts expected, which is reassuring since population stabilisation will occur earlier than projected estimates.
Second, the Muslim population has increased from 13.4 per cent of the population to 14.2 per cent, which is 0.8 percentage points higher. But the rate of growth is considerably lower than in previous decades. Muslims are expected to grow faster than Hindus for a couple of more decades because they have the youngest median age and relatively high fertility among the major religious groups in India. In 2010, the median age of Indian Muslims was 22, compared with 26 for Hindus and 28 for Christians. Muslim women bear an average 3.1 children per head, compared with 2.7 for Hindus and 2.3 for Christians.
Third, in 2011, Hindus constituted 79.8 per cent of the population, compared to 80.5 per cent in 2001. This is the result of a rate of decline over the decade of 3.5 percentage points. It is the difference between the decadal growth rate of Hindus in 2001, which was 20.3 per cent and their growth rate between 2001 and 2011, which is 16.8 per cent. Compare these with the ratios for Muslims, who had a decadal growth rate of 29.5 per cent in 2001. This growth rate, between 2001 and 2011, has declined steeply to 24.6 per cent. This decline works out to be a high 4.9 percentage points.
Fourth,
when these percentage point declines are compared between Hindus and Muslims, Muslims have shown a 50 per cent higher decline in growth rate than Hindus. This positive higher decline of Muslims compared with Hindus has been occurring since 1981, and is expected to continue in a manner such that the Muslim growth rate will soon be similar to that of the Hindus. The fast pace of decline in Muslim women’s fertility rate is occurring while they have a much lower mean child-bearing age, which in itself is evidence that falling Muslim fertility is choice-based and irreversible in the near future.
Fifth, overall, there is considerable improvement in the sex ratio in 2011 — 943. This improvement has been phenomenal among Hindus. This is a very positive story of Census 2011. Yet, Muslims have better sex ratios compared to Hindus, which is also a contributing factor in the relatively higher number of births.
Sixth, it has been pointed out since the mid-1980s that the prevalence rate of contraceptives among Muslims has been increasing faster than among Hindus and is likely to catch up with the national average earlier than expected. The rate of increase in contraception among the Muslim community, even in states like Uttar Pradesh, Bihar and West Bengal, has been high.
