Skandapurana 6.3.10.54

6.3.10.54

keciddvādaśabhirvarṣaiḥ ṣaḍbharanye tapodhanāḥ .
tribhiḥ saṃvatsaraiḥ kecitkecitsaṃvatsareṇa tu .. 10.54 ..

Some ascetics [attained perfection] in twelve years, others in six, / some in three years, and some in a single year;