The 4th as well as the 6th-Case-affix may be used, when blessing is intended in connection with the words āyuṣa 'long life', madra 'joy', bhadra 'good fortune', kuśala 'welfare', sukha 'happiness', artha 'prosperity' and hita 'good'.,
The च in the sutra makes the employment of Dative optional : in the alternative we have Genitive.
Vart:- In this sutra आयुष्य &c., include their synonyms also.
Thus आयुष्यं देवदत्ताय भूयात् or आयुष्यं देवदत्तस्य भूयात् ॥ Similarly चिरं जीवितं, मद्रं, भद्रं, कुशलं, निरामयं, सुखं, शं, अर्थो, प्रयोजनं, हितं पथ्यं देवदत्ताय or देवदत्तस्य भूयात् ॥
Why do we say when 'benediction is intended'? Observe आयुष्यं देवदत्तस्य तपः 'the austerity is the cause of the long life of Devadatta.' Here there is no option allowed : and the Genitive case is only employed.,