Is it permissible to slaughter a small calf (veal) as an ‘Aqīqah for a male newborn instead of two sheep, or is the slaughter of two sheep obligatory?

For the aqiqah with cattle, it is stipulated that the animal must have reached the age prescribed for validity, which is two years and entering the third. The calf mentioned in the question is not sufficient because it has not reached the valid age. The fundamental sunnah for aqiqah is fulfilled by sacrificing a sheep. One-seventh of a cow or one-seventh of a camel is also sufficient in place of a sheep, and this is the view of the Shafiis.