यत्तु प्रत्युपकारार्थं फलमुद्दिश्य वा पुनः। दीयते च परिक्लिष्टं तद्दानं राजसं स्मृतम् ॥

yat tu pratyupakārārthaṁ phalam uddiśhya vā punaḥ dīyate cha parikliṣhṭaṁ tad dānaṁ rājasaṁ smṛitam

That given with a view to receiving in return, or looking for fruit again, or grudgingly, that alms is accounted of passion.

In plain words: A gift comes from passion when it is given to get something back, to win a reward, or when it is given unwillingly.